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AT&T 3B computer systems included the 3B2, 3B5, 3B15, 3B20S, and 3B4000. These computers were named after the successful 3B20D. The 3B20S (simplex) ran using the UNIX operating system and was developed at Bell Labs and produced by WECo in 1982 for the general purpose internal Bell System use, and later the mini-computer market.
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mdadm(8) [bsd man page]

MDADM(8)						      System Manager's Manual							  MDADM(8)

NAME
       mdadm - manage MD devices aka Linux Software RAID

SYNOPSIS
       mdadm [mode] <raiddevice> [options] <component-devices>

DESCRIPTION
       RAID  devices are virtual devices created from two or more real block devices.  This allows multiple devices (typically disk drives or par-
       titions thereof) to be combined into a single device to hold (for example) a single filesystem.	Some RAID levels include redundancy and so
       can survive some degree of device failure.

       Linux Software RAID devices are implemented through the md (Multiple Devices) device driver.

       Currently,  Linux supports LINEAR md devices, RAID0 (striping), RAID1 (mirroring), RAID4, RAID5, RAID6, RAID10, MULTIPATH, FAULTY, and CON-
       TAINER.

       MULTIPATH is not a Software RAID mechanism, but does involve multiple devices: each device is a path to one common physical storage device.
       New installations should not use md/multipath as it is not well supported and has no ongoing development.  Use the Device Mapper based mul-
       tipath-tools instead.

       FAULTY is also not true RAID, and it only involves one device.  It provides a layer over a true device that can be used to inject faults.

       CONTAINER is different again.  A CONTAINER is a collection of devices that are managed as a set.  This is similar to  the  set  of  devices
       connected  to a hardware RAID controller.  The set of devices may contain a number of different RAID arrays each utilising some (or all) of
       the blocks from a number of the devices in the set.  For example, two devices in a 5-device set might form a RAID1 using the whole devices.
       The remaining three might have a RAID5 over the first half of each device, and a RAID0 over the second half.

       With  a	CONTAINER,  there  is  one  set  of metadata that describes all of the arrays in the container.  So when mdadm creates a CONTAINER
       device, the device just represents the metadata.  Other normal arrays (RAID1 etc) can be created inside the container.

MODES
       mdadm has several major modes of operation:

       Assemble
	      Assemble the components of a previously created array into an active array.  Components can be explicitly given or can  be  searched
	      for.  mdadm checks that the components do form a bona fide array, and can, on request, fiddle superblock information so as to assem-
	      ble a faulty array.

       Build  Build an array that doesn't have per-device metadata (superblocks).  For these sorts of arrays, mdadm cannot  differentiate  between
	      initial  creation  and  subsequent  assembly  of	an array.  It also cannot perform any checks that appropriate components have been
	      requested.  Because of this, the Build mode should only be used together with a complete understanding of what you are doing.

       Create Create a new array with per-device metadata (superblocks).  Appropriate metadata is written to each device, and then the array  com-
	      prising  those  devices is activated.  A 'resync' process is started to make sure that the array is consistent (e.g. both sides of a
	      mirror contain the same data) but the content of the device is left otherwise untouched.	The array can be used as soon  as  it  has
	      been created.  There is no need to wait for the initial resync to finish.

       Follow or Monitor
	      Monitor one or more md devices and act on any state changes.  This is only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as
	      only these have interesting state.  RAID0 or Linear never have missing, spare, or failed drives, so there is nothing to monitor.

       Grow   Grow (or shrink) an array, or otherwise reshape it in some way.  Currently supported growth options including  changing  the  active
	      size  of	component  devices  and changing the number of active devices in Linear and RAID levels 0/1/4/5/6, changing the RAID level
	      between 0, 1, 5, and 6, and between 0 and 10, changing the chunk size and layout for RAID 0,4,5,6,10 as well as adding or removing a
	      write-intent bitmap and changing the array's consistency policy.

       Incremental Assembly
	      Add  a  single  device  to an appropriate array.	If the addition of the device makes the array runnable, the array will be started.
	      This provides a convenient interface to a hot-plug system.  As each device is detected, mdadm has a chance to  include  it  in  some
	      array  as  appropriate.	Optionally,  when  the --fail flag is passed in we will remove the device from any active array instead of
	      adding it.

	      If a CONTAINER is passed to mdadm in this mode, then any arrays within that container will be assembled and started.

       Manage This is for doing things to specific components of an array such as adding new spares and removing faulty devices.

       Misc   This is an 'everything else' mode that supports operations on active arrays, operations on component devices  such  as  erasing  old
	      superblocks, and information gathering operations.

       Auto-detect
	      This mode does not act on a specific device or array, but rather it requests the Linux Kernel to activate any auto-detected arrays.

OPTIONS
Options for selecting a mode are:
       -A, --assemble
	      Assemble a pre-existing array.

       -B, --build
	      Build a legacy array without superblocks.

       -C, --create
	      Create a new array.

       -F, --follow, --monitor
	      Select Monitor mode.

       -G, --grow
	      Change the size or shape of an active array.

       -I, --incremental
	      Add/remove a single device to/from an appropriate array, and possibly start the array.

       --auto-detect
	      Request  that  the  kernel  starts any auto-detected arrays.  This can only work if md is compiled into the kernel -- not if it is a
	      module.  Arrays can be auto-detected by the kernel if all the components are in primary MS-DOS partitions with  partition  type  FD,
	      and  all	use  v0.90  metadata.	In-kernel autodetect is not recommended for new installations.	Using mdadm to detect and assemble
	      arrays -- possibly in an initrd -- is substantially more flexible and should be preferred.

       If a device is given before any options, or if the first option is one of --add, --re-add, --add-spare,	--fail,  --remove,  or	--replace,
       then the MANAGE mode is assumed.  Anything other than these will cause the Misc mode to be assumed.

Options that are not mode-specific are:
       -h, --help
	      Display general help message or, after one of the above options, a mode-specific help message.

       --help-options
	      Display more detailed help about command line parsing and some commonly used options.

       -V, --version
	      Print version information for mdadm.

       -v, --verbose
	      Be  more	verbose  about what is happening.  This can be used twice to be extra-verbose.	The extra verbosity currently only affects
	      --detail --scan and --examine --scan.

       -q, --quiet
	      Avoid printing purely informative messages.  With this, mdadm will be silent unless there is something really important to report.

       -f, --force
	      Be more forceful about certain operations.  See the various modes for the exact meaning of this option in different contexts.

       -c, --config=
	      Specify the config file or directory.  Default is to use /etc/mdadm/mdadm.conf and /etc/mdadm/mdadm.conf.d, or if those are  missing
	      then /etc/mdadm.conf and /etc/mdadm.conf.d.  If the config file given is partitions then nothing will be read, but mdadm will act as
	      though the config file contained exactly
		  DEVICE partitions containers
	      and will read /proc/partitions to find a list of devices to scan, and /proc/mdstat to find a list of containers to examine.  If  the
	      word none is given for the config file, then mdadm will act as though the config file were empty.

	      If  the  name given is of a directory, then mdadm will collect all the files contained in the directory with a name ending in .conf,
	      sort them lexically, and process all of those files as config files.

       -s, --scan
	      Scan config file or /proc/mdstat for missing information.  In general, this option gives mdadm permission to get any missing  infor-
	      mation  (like  component	devices, array devices, array identities, and alert destination) from the configuration file (see previous
	      option); one exception is MISC mode when using --detail or --stop, in which case --scan says to get a list  of  array  devices  from
	      /proc/mdstat.

       -e, --metadata=
	      Declare  the  style  of  RAID metadata (superblock) to be used.  The default is 1.2 for --create, and to guess for other operations.
	      The default can be overridden by setting the metadata value for the CREATE keyword in mdadm.conf.

	      Options are:

	      0, 0.90
		     Use the original 0.90 format superblock.  This format limits arrays to 28 component devices and limits component  devices	of
		     levels 1 and greater to 2 terabytes.  It is also possible for there to be confusion about whether the superblock applies to a
		     whole device or just the last partition, if that partition starts on a 64K boundary.

	      1, 1.0, 1.1, 1.2 default
		     Use the new version-1 format superblock.  This has fewer restrictions.  It can easily be moved between hosts  with  different
		     endian-ness,  and a recovery operation can be checkpointed and restarted.	The different sub-versions store the superblock at
		     different locations on the device, either at the end (for 1.0), at the start (for 1.1) or 4K from the start (for  1.2).   "1"
		     is equivalent to "1.2" (the commonly preferred 1.x format).  "default" is equivalent to "1.2".

	      ddf    Use  the  "Industry  Standard"  DDF (Disk Data Format) format defined by SNIA.  When creating a DDF array a CONTAINER will be
		     created, and normal arrays can be created in that container.

	      imsm   Use the Intel(R) Matrix Storage Manager metadata format.  This creates a CONTAINER which is managed in a  similar	manner	to
		     DDF, and is supported by an option-rom on some platforms:

		     http://www.intel.com/design/chipsets/matrixstorage_sb.htm

       --homehost=
	      This will override any HOMEHOST setting in the config file and provides the identity of the host which should be considered the home
	      for any arrays.

	      When creating an array, the homehost will be recorded in the metadata.  For version-1 superblocks, it will be prefixed to the  array
	      name.  For version-0.90 superblocks, part of the SHA1 hash of the hostname will be stored in the later half of the UUID.

	      When reporting information about an array, any array which is tagged for the given homehost will be reported as such.

	      When  using  Auto-Assemble,  only  arrays tagged for the given homehost will be allowed to use 'local' names (i.e. not ending in '_'
	      followed by a digit string).  See below under Auto Assembly.

	      The special name "any" can be used as a wild card.  If an array is created with --homehost=any then the name "any" will be stored in
	      the  array  and  it  can	be  assembled  in  the same way on any host.  If an array is assembled with this option, then the homehost
	      recorded on the array will be ignored.

       --prefer=
	      When mdadm needs to print the name for a device it normally finds the name in /dev which refers to the device and is shortest.  When
	      a path component is given with --prefer mdadm will prefer a longer name if it contains that component.  For example --prefer=by-uuid
	      will prefer a name in a subdirectory of /dev called by-uuid.

	      This functionality is currently only provided by --detail and --monitor.

       --home-cluster=
	      specifies the cluster name for the md device. The md device can be assembled only on the cluster which matches the  name	specified.
	      If this option is not provided, mdadm tries to detect the cluster name automatically.

For create, build, or grow:
       -n, --raid-devices=
	      Specify the number of active devices in the array.  This, plus the number of spare devices (see below) must equal the number of com-
	      ponent-devices (including "missing" devices) that are listed on the command line for --create.  Setting a value of 1 is  probably  a
	      mistake  and so requires that --force be specified first.  A value of 1 will then be allowed for linear, multipath, RAID0 and RAID1.
	      It is never allowed for RAID4, RAID5 or RAID6.
	      This number can only be changed using --grow for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide the  neces-
	      sary support.

       -x, --spare-devices=
	      Specify the number of spare (eXtra) devices in the initial array.  Spares can also be added and removed later.  The number of compo-
	      nent devices listed on the command line must equal the number of RAID devices plus the number of spare devices.

       -z, --size=
	      Amount (in Kilobytes) of space to use from each drive in RAID levels 1/4/5/6.  This must be a multiple of the chunk size,  and  must
	      leave  about  128Kb  of space at the end of the drive for the RAID superblock.  If this is not specified (as it normally is not) the
	      smallest drive (or partition) sets the size, though if there is a variance among the drives of greater than 1%, a warning is issued.

	      A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or Gigabytes respectively.

	      Sometimes a replacement drive can be a little smaller than the original drives though this should be minimised by  IDEMA	standards.
	      Such  a  replacement  drive will be rejected by md.  To guard against this it can be useful to set the initial size slightly smaller
	      than the smaller device with the aim that it will still be larger than any replacement.

	      This value can be set with --grow for RAID level 1/4/5/6 though CONTAINER based arrays such as those with IMSM metadata may  not	be
	      able  to	support  this.	 If  the  array  was  created with a size smaller than the currently active drives, the extra space can be
	      accessed using --grow.  The size can be given as max which means to choose the largest size that fits on all current drives.

	      Before reducing the size of the array (with --grow --size=) you should make sure that space isn't needed.  If  the  device  holds  a
	      filesystem, you would need to resize the filesystem to use less space.

	      After  reducing  the  array  size  you  should  check  that the data stored in the device is still available.  If the device holds a
	      filesystem, then an 'fsck' of the filesystem is a minimum requirement.  If there are problems the array can  be  made  bigger  again
	      with no loss with another --grow --size= command.

	      This  value  cannot be used when creating a CONTAINER such as with DDF and IMSM metadata, though it perfectly valid when creating an
	      array inside a container.

       -Z, --array-size=
	      This is only meaningful with --grow and its effect is not persistent: when the array is stopped and restarted the default array size
	      will be restored.

	      Setting  the  array-size	causes	the  array to appear smaller to programs that access the data.	This is particularly needed before
	      reshaping an array so that it will be smaller.  As the reshape is not reversible, but setting the size with --array-size is,  it	is
	      required that the array size is reduced as appropriate before the number of devices in the array is reduced.

	      Before  reducing	the  size  of the array you should make sure that space isn't needed.  If the device holds a filesystem, you would
	      need to resize the filesystem to use less space.

	      After reducing the array size you should check that the data stored in the device  is  still  available.	 If  the  device  holds  a
	      filesystem,  then  an  'fsck'  of the filesystem is a minimum requirement.  If there are problems the array can be made bigger again
	      with no loss with another --grow --array-size= command.

	      A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or Gigabytes respectively.  A value of	max  restores  the
	      apparent size of the array to be whatever the real amount of available space is.

	      Clustered arrays do not support this parameter yet.

       -c, --chunk=
	      Specify  chunk  size of kilobytes.  The default when creating an array is 512KB.	To ensure compatibility with earlier versions, the
	      default when building an array with no persistent metadata is 64KB.  This is only meaningful for RAID0,  RAID4,  RAID5,  RAID6,  and
	      RAID10.

	      RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power of 2.  In any case it must be a multiple of 4KB.

	      A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or Gigabytes respectively.

       --rounding=
	      Specify  rounding factor for a Linear array.  The size of each component will be rounded down to a multiple of this size.  This is a
	      synonym for --chunk but highlights the different meaning for Linear as compared to other RAID levels.  The default is 64K if a  ker-
	      nel earlier than 2.6.16 is in use, and is 0K (i.e. no rounding) in later kernels.

       -l, --level=
	      Set  RAID  level.   When	used with --create, options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4, raid5, 5, raid6, 6,
	      raid10, 10, multipath, mp, faulty, container.  Obviously some of these are synonymous.

	      When a CONTAINER metadata type is requested, only the container level is permitted, and it does not need to be explicitly given.

	      When used with --build, only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.

	      Can be used with --grow to change the RAID level in some cases.  See LEVEL CHANGES below.

       -p, --layout=
	      This option configures the fine details of data layout for RAID5, RAID6, and RAID10 arrays,  and	controls  the  failure	modes  for
	      faulty.

	      The  layout  of the RAID5 parity block can be one of left-asymmetric, left-symmetric, right-asymmetric, right-symmetric, la, ra, ls,
	      rs.  The default is left-symmetric.

	      It is also possible to cause RAID5 to use a RAID4-like layout by choosing parity-first, or parity-last.

	      Finally for RAID5 there are DDF-compatible layouts, ddf-zero-restart, ddf-N-restart, and ddf-N-continue.

	      These same layouts are available for RAID6.  There are also 4 layouts that will provide an intermediate stage for converting between
	      RAID5  and RAID6.  These provide a layout which is identical to the corresponding RAID5 layout on the first N-1 devices, and has the
	      'Q' syndrome (the second 'parity' block used by RAID6) on the last device.  These layouts are: left-symmetric-6,	right-symmetric-6,
	      left-asymmetric-6, right-asymmetric-6, and parity-first-6.

	      When  setting  the  failure  mode  for level faulty, the options are: write-transient, wt, read-transient, rt, write-persistent, wp,
	      read-persistent, rp, write-all, read-fixable, rf, clear, flush, none.

	      Each failure mode can be followed by a number, which is used as a period between fault generation.  Without a number, the  fault	is
	      generated  once  on  the first relevant request.	With a number, the fault will be generated after that many requests, and will con-
	      tinue to be generated every time the period elapses.

	      Multiple failure modes can be current simultaneously by using the --grow option to set subsequent failure modes.

	      "clear" or "none" will remove any pending or periodic failure modes, and "flush" will clear any persistent faults.

	      Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed by a small number.  The default is 'n2'.   The  supported
	      options are:

	      'n' signals 'near' copies.  Multiple copies of one data block are at similar offsets in different devices.

	      'o'  signals 'offset' copies.  Rather than the chunks being duplicated within a stripe, whole stripes are duplicated but are rotated
	      by one device so duplicate blocks are on different devices.  Thus subsequent copies of a block are in the next drive,  and  are  one
	      chunk further down.

	      'f'  signals  'far'  copies  (multiple  copies  have very different offsets).  See md(4) for more detail about 'near', 'offset', and
	      'far'.

	      The number is the number of copies of each datablock.  2 is normal, 3 can be useful.  This number can be at most equal to the number
	      of  devices in the array.  It does not need to divide evenly into that number (e.g. it is perfectly legal to have an 'n2' layout for
	      an array with an odd number of devices).

	      When an array is converted between RAID5 and RAID6 an intermediate RAID6 layout is used in which the  second  parity  block  (Q)	is
	      always  on  the  last  device.  To convert a RAID5 to RAID6 and leave it in this new layout (which does not require re-striping) use
	      --layout=preserve.  This will try to avoid any restriping.

	      The converse of this is --layout=normalise which will change a non-standard RAID6 layout into a more standard arrangement.

       --parity=
	      same as --layout (thus explaining the p of -p).

       -b, --bitmap=
	      Specify a file to store a write-intent bitmap in.  The file should not exist unless --force is also given.  The same file should	be
	      provided when assembling the array.  If the word internal is given, then the bitmap is stored with the metadata on the array, and so
	      is replicated on all devices.  If the word none is given with --grow mode, then any bitmap that is present is removed. If  the  word
	      clustered  is given, the array is created for a clustered environment. One bitmap is created for each node as defined by the --nodes
	      parameter and are stored internally.

	      To help catch typing errors, the filename must contain at least one slash ('/') if it is a real file (not 'internal' or 'none').

	      Note: external bitmaps are only known to work on ext2 and ext3.  Storing bitmap files on other filesystems  may  result  in  serious
	      problems.

	      When  creating an array on devices which are 100G or larger, mdadm automatically adds an internal bitmap as it will usually be bene-
	      ficial.  This can be suppressed with --bitmap=none or by selecting a different consistency policy with --consistency-policy.

       --bitmap-chunk=
	      Set the chunksize of the bitmap.	Each bit corresponds to that many Kilobytes of storage.  When  using  a  file  based  bitmap,  the
	      default  is  to  use the smallest size that is at-least 4 and requires no more than 2^21 chunks.	When using an internal bitmap, the
	      chunksize defaults to 64Meg, or larger if necessary to fit the bitmap into the available space.

	      A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or Gigabytes respectively.

       -W, --write-mostly
	      subsequent devices listed in a --build, --create, or --add command will be flagged as 'write-mostly'.  This is valid for RAID1  only
	      and  means  that	the  'md' driver will avoid reading from these devices if at all possible.  This can be useful if mirroring over a
	      slow link.

       --write-behind=
	      Specify that write-behind mode should be enabled (valid for RAID1 only).	If an argument is specified, it will set the maximum  num-
	      ber  of outstanding writes allowed.  The default value is 256.  A write-intent bitmap is required in order to use write-behind mode,
	      and write-behind is only attempted on drives marked as write-mostly.

       --failfast
	      subsequent devices listed in a --create or --add command will be flagged as  'failfast'.	This is valid for RAID1 and  RAID10  only.
	      IO  requests  to	these  devices	will  be  encouraged to fail quickly rather than cause long delays due to error handling.  Also no
	      attempt is made to repair a read error on these devices.

	      If an array becomes degraded so that the 'failfast' device is the only usable device, the 'failfast' flag will then be  ignored  and
	      extended delays will be preferred to complete failure.

	      The  'failfast'  flag  is appropriate for storage arrays which have a low probability of true failure, but which may sometimes cause
	      unacceptable delays due to internal maintenance functions.

       --assume-clean
	      Tell mdadm that the array pre-existed and is known to be clean.  It can be useful when trying to recover from a major failure as you
	      can  be  sure  that  no  data will be affected unless you actually write to the array.  It can also be used when creating a RAID1 or
	      RAID10 if you want to avoid the initial resync, however this practice -- while normally safe -- is not recommended.  Use	this  only
	      if you really know what you are doing.

	      When  the  devices  that will be part of a new array were filled with zeros before creation the operator knows the array is actually
	      clean. If that is the case, such as after running badblocks, this argument can be used to tell mdadm the facts the operator knows.

	      When an array is resized to a larger size with --grow --size= the new space is normally resynced in that same  way  that	the  whole
	      array is resynced at creation.  From Linux version 3.0, --assume-clean can be used with that command to avoid the automatic resync.

       --backup-file=
	      This  is	needed when --grow is used to increase the number of raid-devices in a RAID5 or RAID6 if there are no spare devices avail-
	      able, or to shrink, change RAID level or layout.	See the GROW MODE section below on RAID-DEVICES CHANGES.  The file must be  stored
	      on a separate device, not on the RAID array being reshaped.

       --data-offset=
	      Arrays with 1.x metadata can leave a gap between the start of the device and the start of array data.  This gap can be used for var-
	      ious metadata.  The start of data is known as the data-offset.  Normally an appropriate data offset is computed automatically.  How-
	      ever  it can be useful to set it explicitly such as when re-creating an array which was originally created using a different version
	      of mdadm which computed a different offset.

	      Setting the offset explicitly over-rides the default.  The value given is in Kilobytes unless a suffix of 'K', 'M' or 'G' is used to
	      explicitly indicate Kilobytes, Megabytes or Gigabytes respectively.

	      Since Linux 3.4, --data-offset can also be used with --grow for some RAID levels (initially on RAID10).  This allows the data-offset
	      to be changed as part of the reshape process.  When the data offset is changed, no backup file is required as the difference in off-
	      sets is used to provide the same functionality.

	      When the new offset is earlier than the old offset, the number of devices in the array cannot shrink.  When it is after the old off-
	      set, the number of devices in the array cannot increase.

	      When creating an array, --data-offset can be specified as variable.  In the case each member device is expected  to  have  a  offset
	      appended	to the name, separated by a colon.  This makes it possible to recreate exactly an array which has varying data offsets (as
	      can happen when different versions of mdadm are used to add different devices).

       --continue
	      This option is complementary to the --freeze-reshape option for assembly. It is needed when --grow operation is interrupted  and	it
	      is not restarted automatically due to --freeze-reshape usage during array assembly.  This option is used together with -G , ( --grow
	      ) command and device for a pending reshape to be continued.  All parameters required for reshape	continuation  will  be	read  from
	      array  metadata.	 If  initial --grow command had required --backup-file= option to be set, continuation option will require to have
	      exactly the same backup file given as well.

	      Any other parameter passed together with --continue option will be ignored.

       -N, --name=
	      Set a name for the array.  This is currently only effective when creating an array with a version-1 superblock, or an array in a DDF
	      container.   The	name  is a simple textual string that can be used to identify array components when assembling.  If name is needed
	      but not specified, it is taken from the basename of the device that is being created.  e.g. when creating /dev/md/home the name will
	      default to home.

       -R, --run
	      Insist  that mdadm run the array, even if some of the components appear to be active in another array or filesystem.  Normally mdadm
	      will ask for confirmation before including such components in an array.  This option causes that question to be suppressed.

       -f, --force
	      Insist that mdadm accept the geometry and layout specified without question.  Normally mdadm will not allow  creation  of  an  array
	      with  only  one  device, and will try to create a RAID5 array with one missing drive (as this makes the initial resync work faster).
	      With --force, mdadm will not try to be so clever.

       -o, --readonly
	      Start the array read only rather than read-write as normal.  No writes will be allowed to the array, and	no  resync,  recovery,	or
	      reshape will be started. It works with Create, Assemble, Manage and Misc mode.

       -a, --auto{=yes,md,mdp,part,p}{NN}
	      Instruct mdadm how to create the device file if needed, possibly allocating an unused minor number.  "md" causes a non-partitionable
	      array to be used (though since Linux 2.6.28, these array devices are in fact partitionable).  "mdp", "part" or "p" causes  a  parti-
	      tionable	array  (2.6 and later) to be used.  "yes" requires the named md device to have a 'standard' format, and the type and minor
	      number will be determined from this.  With mdadm 3.0, device creation is normally left up to udev so this option is unlikely  to	be
	      needed.  See DEVICE NAMES below.

	      The argument can also come immediately after "-a".  e.g. "-ap".

	      If --auto is not given on the command line or in the config file, then the default will be --auto=yes.

	      If --scan is also given, then any auto= entries in the config file will override the --auto instruction given on the command line.

	      For  partitionable arrays, mdadm will create the device file for the whole array and for the first 4 partitions.	A different number
	      of partitions can be specified at the end of this option (e.g.  --auto=p7).  If the device name ends with  a  digit,  the  partition
	      names  add  a  'p', and a number, e.g.  /dev/md/home1p3.	If there is no trailing digit, then the partition names just have a number
	      added, e.g.  /dev/md/scratch3.

	      If the md device name is in a 'standard' format as described in DEVICE NAMES, then it will be created, if necessary, with the appro-
	      priate  device  number  based  on that name.  If the device name is not in one of these formats, then a unused device number will be
	      allocated.  The device number will be considered unused if there is no active array for that number, and there is no entry  in  /dev
	      for that number and with a non-standard name.  Names that are not in 'standard' format are only allowed in "/dev/md/".

	      This is meaningful with --create or --build.

       -a, --add
	      This option can be used in Grow mode in two cases.

	      If the target array is a Linear array, then --add can be used to add one or more devices to the array.  They are simply catenated on
	      to the end of the array.	Once added, the devices cannot be removed.

	      If the --raid-disks option is being used to increase the number of devices in an array, then --add can be used  to  add  some  extra
	      devices  to  be included in the array.  In most cases this is not needed as the extra devices can be added as spares first, and then
	      the number of raid-disks can be changed.	However for RAID0, it is not possible to add spares.  So to increase the number of devices
	      in a RAID0, it is necessary to set the new number of devices, and to add the new devices, in the same command.

       --nodes
	      Only  works  when the array is for clustered environment. It specifies the maximum number of nodes in the cluster that will use this
	      device simultaneously. If not specified, this defaults to 4.

       --write-journal
	      Specify journal device for the RAID-4/5/6 array. The journal device should be a SSD with reasonable lifetime.

       --symlinks
	      Auto creation of symlinks in /dev to /dev/md, option --symlinks must be 'no' or 'yes' and work with --create and --build.

       -k, --consistency-policy=
	      Specify how the array maintains consistency in case of unexpected shutdown.  Only relevant for RAID levels  with	redundancy.   Cur-
	      rently supported options are:

	      resync Full resync is performed and all redundancy is regenerated when the array is started after unclean shutdown.

	      bitmap Resync assisted by a write-intent bitmap. Implicitly selected when using --bitmap.

	      journal
		     For RAID levels 4/5/6, journal device is used to log transactions and replay after unclean shutdown. Implicitly selected when
		     using --write-journal.

	      ppl    For RAID5 only, Partial Parity Log is used to close the write hole and eliminate resync. PPL is stored in the metadata region
		     of RAID member drives, no additional journal drive is needed.

	      Can be used with --grow to change the consistency policy of an active array in some cases. See CONSISTENCY POLICY CHANGES below.

For assemble:
       -u, --uuid=
	      uuid of array to assemble.  Devices which don't have this uuid are excluded

       -m, --super-minor=
	      Minor number of device that array was created for.  Devices which don't have this minor number are excluded.  If you create an array
	      as /dev/md1, then all superblocks will contain the minor number 1, even if the array is later assembled as /dev/md2.

	      Giving the literal word "dev" for --super-minor will cause mdadm to use the minor number of the md device that is  being	assembled.
	      e.g. when assembling /dev/md0, --super-minor=dev will look for super blocks with a minor number of 0.

	      --super-minor is only relevant for v0.90 metadata, and should not normally be used.  Using --uuid is much safer.

       -N, --name=
	      Specify  the name of the array to assemble.  This must be the name that was specified when creating the array.  It must either match
	      the name stored in the superblock exactly, or it must match with the current homehost prefixed to the start of the given name.

       -f, --force
	      Assemble the array even if the metadata on some devices appears to be out-of-date.  If mdadm cannot find enough working  devices	to
	      start  the  array,  but can find some devices that are recorded as having failed, then it will mark those devices as working so that
	      the array can be started.  An array which requires --force to be started may contain data corruption.  Use it carefully.

       -R, --run
	      Attempt to start the array even if fewer drives were given than were present last time the array was active.  Normally  if  not  all
	      the  expected drives are found and --scan is not used, then the array will be assembled but not started.	With --run an attempt will
	      be made to start it anyway.

       --no-degraded
	      This is the reverse of --run in that it inhibits the startup of array unless all expected drives are present.  This is  only  needed
	      with --scan, and can be used if the physical connections to devices are not as reliable as you would like.

       -a, --auto{=no,yes,md,mdp,part}
	      See this option under Create and Build options.

       -b, --bitmap=
	      Specify  the bitmap file that was given when the array was created.  If an array has an internal bitmap, there is no need to specify
	      this when assembling the array.

       --backup-file=
	      If --backup-file was used while reshaping an array (e.g. changing number of devices or chunk size) and the system crashed during the
	      critical	section,  then the same --backup-file must be presented to --assemble to allow possibly corrupted data to be restored, and
	      the reshape to be completed.

       --invalid-backup
	      If the file needed for the above option is not available for any reason an empty file can be given  together  with  this	option	to
	      indicate	that  the  backup  file  is  invalid.	In  this case the data that was being rearranged at the time of the crash could be
	      irrecoverably lost, but the rest of the array may still be recoverable.  This option should only be used as a last resort  if  there
	      is no way to recover the backup file.

       -U, --update=
	      Update the superblock on each device while assembling the array.	The argument given to this flag can be one of sparc2.2, summaries,
	      uuid, name, nodes, homehost, home-cluster, resync,  byteorder,  devicesize,  no-bitmap,  bbl,  no-bbl,  ppl,  no-ppl,  metadata,	or
	      super-minor.

	      The  sparc2.2  option will adjust the superblock of an array what was created on a Sparc machine running a patched 2.2 Linux kernel.
	      This kernel got the alignment of part of the superblock wrong.  You can use the --examine --sparc2.2 option to  mdadm  to  see  what
	      effect this would have.

	      The  super-minor option will update the preferred minor field on each superblock to match the minor number of the array being assem-
	      bled.  This can be useful if --examine reports a different "Preferred Minor" to --detail.  In some cases this update  will  be  per-
	      formed  automatically  by  the  kernel  driver.	In particular the update happens automatically at the first write to an array with
	      redundancy (RAID level 1 or greater) on a 2.6 (or later) kernel.

	      The uuid option will change the uuid of the array.  If a UUID is given with the --uuid option that UUID will be used as a  new  UUID
	      and will NOT be used to help identify the devices in the array.  If no --uuid is given, a random UUID is chosen.

	      The name option will change the name of the array as stored in the superblock.  This is only supported for version-1 superblocks.

	      The nodes option will change the nodes of the array as stored in the bitmap superblock. This option only works for a clustered envi-
	      ronment.

	      The homehost option will change the homehost as recorded in the superblock.  For version-0 superblocks, this is the same as updating
	      the UUID.  For version-1 superblocks, this involves updating the name.

	      The  home-cluster option will change the cluster name as recorded in the superblock and bitmap. This option only works for clustered
	      environment.

	      The resync option will cause the array to be marked dirty meaning that any redundancy in the array (e.g. parity  for  RAID5,  copies
	      for RAID1) may be incorrect.  This will cause the RAID system to perform a "resync" pass to make sure that all redundant information
	      is correct.

	      The byteorder option allows arrays to be moved between machines with different byte-order, such as from a big-endian machine like  a
	      Sparc or some MIPS machines, to a little-endian x86_64 machine.  When assembling such an array for the first time after a move, giv-
	      ing --update=byteorder will cause mdadm to expect superblocks to have their byteorder reversed, and will correct that  order  before
	      assembling the array.  This is only valid with original (Version 0.90) superblocks.

	      The  summaries option will correct the summaries in the superblock.  That is the counts of total, working, active, failed, and spare
	      devices.

	      The devicesize option will rarely be of use.  It applies to version 1.1 and 1.2 metadata only (where the metadata is at the start of
	      the device) and is only useful when the component device has changed size (typically become larger).  The version 1 metadata records
	      the amount of the device that can be used to store data, so if a device in a version 1.1 or 1.2 array becomes larger,  the  metadata
	      will  still  be  visible, but the extra space will not.  In this case it might be useful to assemble the array with --update=device-
	      size.  This will cause mdadm to determine the maximum usable amount of space on each device and update the  relevant  field  in  the
	      metadata.

	      The  metadata  option only works on v0.90 metadata arrays and will convert them to v1.0 metadata.  The array must not be dirty (i.e.
	      it must not need a sync) and it must not have a write-intent bitmap.

	      The old metadata will remain on the devices, but will appear older than the new metadata and so will usually  be	ignored.  The  old
	      metadata (or indeed the new metadata) can be removed by giving the appropriate --metadata= option to --zero-superblock.

	      The no-bitmap option can be used when an array has an internal bitmap which is corrupt in some way so that assembling the array nor-
	      mally fails.  It will cause any internal bitmap to be ignored.

	      The bbl option will reserve space in each device for a bad block list.  This will be 4K in size and positioned near the end  of  any
	      free space between the superblock and the data.

	      The  no-bbl  option will cause any reservation of space for a bad block list to be removed.  If the bad block list contains entries,
	      this will fail, as removing the list could cause data corruption.

	      The ppl option will enable PPL for a RAID5 array and reserve space for PPL on each device. There must be enough free  space  between
	      the data and superblock and a write-intent bitmap or journal must not be used.

	      The no-ppl option will disable PPL in the superblock.

       --freeze-reshape
	      Option  is  intended  to	be used in start-up scripts during initrd boot phase.  When array under reshape is assembled during initrd
	      phase, this option stops reshape after reshape critical section is being restored. This happens before file system  pivot  operation
	      and avoids loss of file system context.  Losing file system context would cause reshape to be broken.

	      Reshape can be continued later using the --continue option for the grow command.

       --symlinks
	      See this option under Create and Build options.

For Manage mode:
       -t, --test
	      Unless  a more serious error occurred, mdadm will exit with a status of 2 if no changes were made to the array and 0 if at least one
	      change was made.	This can be useful when an indirect specifier such as missing, detached or faulty is used in requesting an  opera-
	      tion on the array.  --test will report failure if these specifiers didn't find any match.

       -a, --add
	      hot-add  listed devices.	If a device appears to have recently been part of the array (possibly it failed or was removed) the device
	      is re-added as described in the next point.  If that fails or the device was never part of the array, the device is added as a  hot-
	      spare.  If the array is degraded, it will immediately start to rebuild data onto that spare.

	      Note that this and the following options are only meaningful on array with redundancy.  They don't apply to RAID0 or Linear.

       --re-add
	      re-add  a device that was previously removed from an array.  If the metadata on the device reports that it is a member of the array,
	      and the slot that it used is still vacant, then the device will be added back to the array in the same position.	This will normally
	      cause  the data for that device to be recovered.	However based on the event count on the device, the recovery may only require sec-
	      tions that are flagged a write-intent bitmap to be recovered or may not require any recovery at all.

	      When used on an array that has no metadata (i.e. it was built with --build) it will be assumed that bitmap-based recovery is  enough
	      to make the device fully consistent with the array.

	      When  used  with	v1.x  metadata,  --re-add  can	be  accompanied by --update=devicesize, --update=bbl, or --update=no-bbl.  See the
	      description of these option when used in Assemble mode for an explanation of their use.

	      If the device name given is missing then mdadm will try to find any device that looks like it should be part of the array but  isn't
	      and will try to re-add all such devices.

	      If  the device name given is faulty then mdadm will find all devices in the array that are marked faulty, remove them and attempt to
	      immediately re-add them.	This can be useful if you are certain that the reason for failure has been resolved.

       --add-spare
	      Add a device as a spare.	This is similar to --add except that it does not attempt --re-add first.  The device will be  added  as  a
	      spare even if it looks like it could be an recent member of the array.

       -r, --remove
	      remove listed devices.  They must not be active.	i.e. they should be failed or spare devices.

	      As  well	as  the  name of a device file (e.g.  /dev/sda1) the words failed, detached and names like set-A can be given to --remove.
	      The first causes all failed device to be removed.  The second causes any device which is no longer connected to the system  (i.e	an
	      'open' returns ENXIO) to be removed.  The third will remove a set as describe below under --fail.

       -f, --fail
	      Mark  listed devices as faulty.  As well as the name of a device file, the word detached or a set name like set-A can be given.  The
	      former will cause any device that has been detached from the system to be marked as failed.  It can then be removed.

	      For RAID10 arrays where the number of copies evenly divides the number of devices, the devices can be conceptually divided into sets
	      where  each set contains a single complete copy of the data on the array.  Sometimes a RAID10 array will be configured so that these
	      sets are on separate controllers.  In this case all the devices in one set can be failed by giving a name like  set-A  or  set-B	to
	      --fail.  The appropriate set names are reported by --detail.

       --set-faulty
	      same as --fail.

       --replace
	      Mark  listed  devices  as  requiring  replacement.   As soon as a spare is available, it will be rebuilt and will replace the marked
	      device.  This is similar to marking a device as faulty, but the device remains in service during the recovery  process  to  increase
	      resilience against multiple failures.  When the replacement process finishes, the replaced device will be marked as faulty.

       --with This  can  follow  a  list of --replace devices.	The devices listed after --with will be preferentially used to replace the devices
	      listed after --replace.  These device must already be spare devices in the array.

       --write-mostly
	      Subsequent devices that are added or re-added will have the 'write-mostly' flag set.  This is only valid for RAID1  and  means  that
	      the 'md' driver will avoid reading from these devices if possible.

       --readwrite
	      Subsequent devices that are added or re-added will have the 'write-mostly' flag cleared.

       --cluster-confirm
	      Confirm  the  existence  of  the	device.  This is issued in response to an --add request by a node in a cluster. When a node adds a
	      device it sends a message to all nodes in the cluster to look for a device with a UUID. This translates to a udev notification  with
	      the  UUID  of  the  device to be added and the slot number. The receiving node must acknowledge this message with --cluster-confirm.
	      Valid arguments are <slot>:<devicename> in case the device is found or <slot>:missing in case the device is not found.

       --add-journal
	      Add journal to an existing array, or recreate journal for RAID-4/5/6 array that lost a journal device.  To  avoid  interrupting  on-
	      going write opertions, --add-journal only works for array in Read-Only state.

       --failfast
	      Subsequent  devices that are added or re-added will have the 'failfast' flag set.  This is only valid for RAID1 and RAID10 and means
	      that the 'md' driver will avoid long timeouts on error handling where possible.

       --nofailfast
	      Subsequent devices that are re-added will be re-added without the 'failfast' flag set.

       Each of these options requires that the first device listed is the array to be acted upon, and the remainder are component  devices  to	be
       added, removed, marked as faulty, etc.  Several different operations can be specified for different devices, e.g.
	    mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
       Each operation applies to all devices listed until the next operation.

       If an array is using a write-intent bitmap, then devices which have been removed can be re-added in a way that avoids a full reconstruction
       but instead just updates the blocks that have changed since the device was removed.  For arrays with persistent metadata (superblocks) this
       is done automatically.  For arrays created with --build mdadm needs to be told that this device we removed recently with --re-add.

       Devices	can  only be removed from an array if they are not in active use, i.e. that must be spares or failed devices.  To remove an active
       device, it must first be marked as faulty.

For Misc mode:
       -Q, --query
	      Examine a device to see (1) if it is an md device and (2) if it is a component of an md array.  Information about what is discovered
	      is presented.

       -D, --detail
	      Print details of one or more md devices.

       --detail-platform
	      Print  details of the platform's RAID capabilities (firmware / hardware topology) for a given metadata format. If used without argu-
	      ment, mdadm will scan all controllers looking for their capabilities. Otherwise, mdadm will only look at the controller specified by
	      the argument in form of an absolute filepath or a link, e.g.  /sys/devices/pci0000:00/0000:00:1f.2.

       -Y, --export
	      When  used with --detail, --detail-platform, --examine, or --incremental output will be formatted as key=value pairs for easy import
	      into the environment.

	      With --incremental The value MD_STARTED indicates whether an array was started (yes) or not, which may  include  a  reason  (unsafe,
	      nothing, no).  Also the value MD_FOREIGN indicates if the array is expected on this host (no), or seems to be from elsewhere (yes).

       -E, --examine
	      Print  contents of the metadata stored on the named device(s).  Note the contrast between --examine and --detail.  --examine applies
	      to devices which are components of an array, while --detail applies to a whole array which is currently active.

       --sparc2.2
	      If an array was created on a SPARC machine with a 2.2 Linux kernel patched with RAID support, the superblock will have been  created
	      incorrectly,  or at least incompatibly with 2.4 and later kernels.  Using the --sparc2.2 flag with --examine will fix the superblock
	      before displaying it.  If this appears to do the right thing,  then  the	array  can  be	successfully  assembled  using	--assemble
	      --update=sparc2.2.

       -X, --examine-bitmap
	      Report information about a bitmap file.  The argument is either an external bitmap file or an array component in case of an internal
	      bitmap.  Note that running this on an array device (e.g.	/dev/md0) does not report the bitmap for that array.

       --examine-badblocks
	      List the bad-blocks recorded for the device, if a bad-blocks list has been configured.  Currently only 1.x  metadata  supports  bad-
	      blocks lists.

       --dump=directory

       --restore=directory
	      Save metadata from lists devices, or restore metadata to listed devices.

       -R, --run
	      start  a	partially  assembled  array.  If --assemble did not find enough devices to fully start the array, it might leaving it par-
	      tially assembled.  If you wish, you can then use --run to start the array in degraded mode.

       -S, --stop
	      deactivate array, releasing all resources.

       -o, --readonly
	      mark array as readonly.

       -w, --readwrite
	      mark array as readwrite.

       --zero-superblock
	      If the device contains a valid md superblock, the block is overwritten with zeros.  With --force	the  block  where  the	superblock
	      would be is overwritten even if it doesn't appear to be valid.

	      Note: Be careful to call --zero-superblock with clustered raid, make sure array isn't used or assembled in other cluster node before
	      execute it.

       --kill-subarray=
	      If the device is a container and the argument to --kill-subarray specifies an inactive subarray in the container, then the  subarray
	      is  deleted.   Deleting  all subarrays will leave an 'empty-container' or spare superblock on the drives.  See --zero-superblock for
	      completely removing a superblock.  Note that some formats depend on the subarray index for generating a UUID, this command will fail
	      if it would change the UUID of an active subarray.

       --update-subarray=
	      If the device is a container and the argument to --update-subarray specifies a subarray in the container, then attempt to update the
	      given superblock field in the subarray. See below in MISC MODE for details.

       -t, --test
	      When used with --detail, the exit status of mdadm is set to reflect the status of the device.  See below in MISC MODE for details.

       -W, --wait
	      For each md device given, wait for any resync, recovery, or reshape activity to finish before returning.	 mdadm	will  return  with
	      success if it actually waited for every device listed, otherwise it will return failure.

       --wait-clean
	      For  each  md  device  given, or each device in /proc/mdstat if --scan is given, arrange for the array to be marked clean as soon as
	      possible.  mdadm will return with success if the array uses external metadata and we successfully waited.  For  native  arrays  this
	      returns  immediately  as	the  kernel handles dirty-clean transitions at shutdown.  No action is taken if safe-mode handling is dis-
	      abled.

       --action=
	      Set the "sync_action" for all md devices given to one of idle, frozen, check, repair.  Setting to idle will abort any currently run-
	      ning  action  though  some  actions will automatically restart.  Setting to frozen will abort any current action and ensure no other
	      action starts automatically.

	      Details of check and repair can be found it md(4) under SCRUBBING AND MISMATCHES.

For Incremental Assembly mode:
       --rebuild-map, -r
	      Rebuild the map file (/run/mdadm/map) that mdadm uses to help track which arrays are currently being assembled.

       --run, -R
	      Run any array assembled as soon as a minimal number of devices are available, rather than waiting until  all  expected  devices  are
	      present.

       --scan, -s
	      Only meaningful with -R this will scan the map file for arrays that are being incrementally assembled and will try to start any that
	      are not already started.	If any such array is listed in mdadm.conf as requiring an external bitmap, that bitmap	will  be  attached
	      first.

       --fail, -f
	      This  allows  the hot-plug system to remove devices that have fully disappeared from the kernel.	It will first fail and then remove
	      the device from any array it belongs to.	The device name given should be a kernel device name such as "sda", not a name in /dev.

       --path=
	      Only used with --fail.  The 'path' given will be recorded so that if a new device appears at the same location it can  be  automati-
	      cally  added  to	the same array.  This allows the failed device to be automatically replaced by a new device without metadata if it
	      appears at specified path.   This option is normally only set by a udev script.

For Monitor mode:
       -m, --mail
	      Give a mail address to send alerts to.

       -p, --program, --alert
	      Give a program to be run whenever an event is detected.

       -y, --syslog
	      Cause all events to be reported through 'syslog'.  The messages have facility of 'daemon' and varying priorities.

       -d, --delay
	      Give a delay in seconds.	mdadm polls the md arrays and then waits this many seconds before polling again.  The default is  60  sec-
	      onds.  Since 2.6.16, there is no need to reduce this as the kernel alerts mdadm immediately when there is any change.

       -r, --increment
	      Give a percentage increment.  mdadm will generate RebuildNN events with the given percentage increment.

       -f, --daemonise
	      Tell  mdadm  to  run  as a background daemon if it decides to monitor anything.  This causes it to fork and run in the child, and to
	      disconnect from the terminal.  The process id of the child is written to stdout.	This is useful with --scan which  will	only  con-
	      tinue monitoring if a mail address or alert program is found in the config file.

       -i, --pid-file
	      When  mdadm is running in daemon mode, write the pid of the daemon process to the specified file, instead of printing it on standard
	      output.

       -1, --oneshot
	      Check arrays only once.  This will generate NewArray events and more significantly DegradedArray and SparesMissing events.  Running
		      mdadm --monitor --scan -1
	      from a cron script will ensure regular notification of any degraded arrays.

       -t, --test
	      Generate a TestMessage alert for every array found at startup.  This alert gets mailed and passed to the alert program.  This can be
	      used for testing that alert message do get through successfully.

       --no-sharing
	      This  inhibits the functionality for moving spares between arrays.  Only one monitoring process started with --scan but without this
	      flag is allowed, otherwise the two could interfere with each other.

ASSEMBLE MODE
       Usage: mdadm --assemble md-device options-and-component-devices...

       Usage: mdadm --assemble --scan md-devices-and-options...

       Usage: mdadm --assemble --scan options...

       This usage assembles one or more RAID arrays from pre-existing components.  For each array, mdadm needs to know the md device, the identity
       of the array, and a number of component-devices.  These can be found in a number of ways.

       In  the	first usage example (without the --scan) the first device given is the md device.  In the second usage example, all devices listed
       are treated as md devices and assembly is attempted.  In the third (where no devices are listed) all md devices that are listed in the con-
       figuration  file  are assembled.  If no arrays are described by the configuration file, then any arrays that can be found on unused devices
       will be assembled.

       If precisely one device is listed, but --scan is not given, then mdadm acts  as	though	--scan	was  given  and  identity  information	is
       extracted from the configuration file.

       The  identity  can be given with the --uuid option, the --name option, or the --super-minor option, will be taken from the md-device record
       in the config file, or will be taken from the super block of the first component-device listed on the command line.

       Devices can be given on the --assemble command line or in the config file.  Only devices which have an md  superblock  which  contains  the
       right identity will be considered for any array.

       The  config  file  is  only  used  if  explicitly  named  with --config or requested with (a possibly implicit) --scan.	In the later case,
       /etc/mdadm/mdadm.conf or /etc/mdadm.conf is used.

       If --scan is not given, then the config file will only be used to find the identity of md arrays.

       Normally the array will be started after it is assembled.  However if --scan is not given and not all expected drives were listed, then the
       array is not started (to guard against usage errors).  To insist that the array be started in this case (as may work for RAID1, 4, 5, 6, or
       10), give the --run flag.

       If udev is active, mdadm does not create any entries in /dev but leaves that to udev.  It does record information in  /run/mdadm/map  which
       will allow udev to choose the correct name.

       If mdadm detects that udev is not configured, it will create the devices in /dev itself.

       In  Linux  kernels prior to version 2.6.28 there were two distinctly different types of md devices that could be created: one that could be
       partitioned using standard partitioning tools and one that could not.  Since 2.6.28 that distinction is no longer relevant as both type	of
       devices	can  be  partitioned.  mdadm will normally create the type that originally could not be partitioned as it has a well defined major
       number (9).

       Prior to 2.6.28, it is important that mdadm chooses the correct type of array device to use.   This  can  be  controlled  with  the  --auto
       option.	In particular, a value of "mdp" or "part" or "p" tells mdadm to use a partitionable device rather than the default.

       In  the	no-udev  case, the value given to --auto can be suffixed by a number.  This tells mdadm to create that number of partition devices
       rather than the default of 4.

       The value given to --auto can also be given in the configuration file as a word starting auto= on the ARRAY line for the relevant array.

   Auto Assembly
       When --assemble is used with --scan and no devices are listed, mdadm will first attempt to assemble all the arrays  listed  in  the  config
       file.

       If no arrays are listed in the config (other than those marked <ignore>) it will look through the available devices for possible arrays and
       will try to assemble anything that it finds.  Arrays which are tagged as belonging to the given homehost will be assembled and started nor-
       mally.	Arrays	which  do not obviously belong to this host are given names that are expected not to conflict with anything local, and are
       started "read-auto" so that nothing is written to any device until the array is written to. i.e.  automatic resync etc is delayed.

       If mdadm finds a consistent set of devices that look like they should comprise an array, and if the superblock is tagged  as  belonging	to
       the  given  home  host, it will automatically choose a device name and try to assemble the array.  If the array uses version-0.90 metadata,
       then the minor number as recorded in the superblock is used to create a name in /dev/md/ so for example /dev/md/3.  If the array uses  ver-
       sion-1  metadata,  then	the  name from the superblock is used to similarly create a name in /dev/md/ (the name will have any 'host' prefix
       stripped first).

       This behaviour can be modified by the AUTO line in the mdadm.conf configuration file.  This line can indicate that specific  metadata  type
       should,	or  should not, be automatically assembled.  If an array is found which is not listed in mdadm.conf and has a metadata format that
       is denied by the AUTO line, then it will not be assembled.  The AUTO line can also request that all arrays identified  as  being  for  this
       homehost should be assembled regardless of their metadata type.	See mdadm.conf(5) for further details.

       Note:  Auto  assembly  cannot  be  used	for  assembling  and  activating  some	arrays which are undergoing reshape.  In particular as the
       backup-file cannot be given, any reshape which requires a backup-file to continue cannot be started by auto assembly.  An  array  which	is
       growing to more devices and has passed the critical section can be assembled using auto-assembly.

BUILD MODE
       Usage: mdadm --build md-device --chunk=X --level=Y --raid-devices=Z devices

       This usage is similar to --create.  The difference is that it creates an array without a superblock.  With these arrays there is no differ-
       ence between initially creating the array and subsequently assembling the array, except that hopefully there is useful data  there  in  the
       second case.

       The  level may raid0, linear, raid1, raid10, multipath, or faulty, or one of their synonyms.  All devices must be listed and the array will
       be started once complete.  It will often be appropriate to use --assume-clean with levels raid1 or raid10.

CREATE MODE
       Usage: mdadm --create md-device --chunk=X --level=Y
		   --raid-devices=Z devices

       This usage will initialise a new md array, associate some devices with it, and activate the array.

       The named device will normally not exist when mdadm --create is run, but will be created by udev once the array becomes active.

       As devices are added, they are checked to see if they contain RAID superblocks or filesystems.  They are also checked to see if	the  vari-
       ance in device size exceeds 1%.

       If any discrepancy is found, the array will not automatically be run, though the presence of a --run can override this caution.

       To  create a "degraded" array in which some devices are missing, simply give the word "missing" in place of a device name.  This will cause
       mdadm to leave the corresponding slot in the array empty.  For a RAID4 or RAID5 array at most one slot can be "missing"; for a RAID6  array
       at most two slots.  For a RAID1 array, only one real device needs to be given.  All of the others can be "missing".

       When  creating  a  RAID5  array,  mdadm will automatically create a degraded array with an extra spare drive.  This is because building the
       spare into a degraded array is in general faster than resyncing the parity on a non-degraded, but not clean, array.  This  feature  can	be
       overridden with the --force option.

       When  creating  an array with version-1 metadata a name for the array is required.  If this is not given with the --name option, mdadm will
       choose a name based on the last component of the name of the device being created.  So if /dev/md3 is being created, then the name  3  will
       be chosen.  If /dev/md/home is being created, then the name home will be used.

       When creating a partition based array, using mdadm with version-1.x metadata, the partition type should be set to 0xDA (non fs-data).  This
       type selection allows for greater precision since using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],  might  create
       problems in the event of array recovery through a live cdrom.

       A  new  array  will  normally  get a randomly assigned 128bit UUID which is very likely to be unique.  If you have a specific need, you can
       choose a UUID for the array by giving the --uuid= option.  Be warned that creating two arrays with the same UUID is a recipe for  disaster.
       Also, using --uuid= when creating a v0.90 array will silently override any --homehost= setting.

       If the array type supports a write-intent bitmap, and if the devices in the array exceed 100G is size, an internal write-intent bitmap will
       automatically be added unless some other option is explicitly requested with the --bitmap option  or  a	different  consistency	policy	is
       selected  with  the --consistency-policy option. In any case space for a bitmap will be reserved so that one can be added later with --grow
       --bitmap=internal.

       If the metadata type supports it (currently only 1.x and IMSM metadata), space will be allocated to store a bad block list.  This allows  a
       modest number of bad blocks to be recorded, allowing the drive to remain in service while only partially functional.

       When  creating  an array within a CONTAINER mdadm can be given either the list of devices to use, or simply the name of the container.  The
       former case gives control over which devices in the container will be used for the array.  The latter case allows  mdadm  to  automatically
       choose which devices to use based on how much spare space is available.

       The General Management options that are valid with --create are:

       --run  insist on running the array even if some devices look like they might be in use.

       --readonly
	      start the array in readonly mode.

MANAGE MODE
       Usage: mdadm device options... devices...

       This usage will allow individual devices in an array to be failed, removed or added.  It is possible to perform multiple operations with on
       command.  For example:
	 mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1
       will firstly mark /dev/hda1 as faulty in /dev/md0 and will then remove it from the array and finally add it back in as  a  spare.   However
       only one md array can be affected by a single command.

       When a device is added to an active array, mdadm checks to see if it has metadata on it which suggests that it was recently a member of the
       array.  If it does, it tries to "re-add" the device.  If there have been no changes since the device was removed, or if	the  array  has  a
       write-intent  bitmap which has recorded whatever changes there were, then the device will immediately become a full member of the array and
       those differences recorded in the bitmap will be resolved.

MISC MODE
       Usage: mdadm options ...  devices ...

       MISC mode includes a number of distinct operations that operate on distinct devices.  The operations are:

       --query
	      The device is examined to see if it is (1) an active md array, or (2) a component of an md array.   The  information  discovered	is
	      reported.

       --detail
	      The device should be an active md device.  mdadm will display a detailed description of the array.  --brief or --scan will cause the
	      output to be less detailed and the format to be suitable for inclusion in mdadm.conf.  The exit status of mdadm will normally  be  0
	      unless mdadm failed to get useful information about the device(s); however, if the --test option is given, then the exit status will
	      be:

	      0      The array is functioning normally.

	      1      The array has at least one failed device.

	      2      The array has multiple failed devices such that it is unusable.

	      4      There was an error while trying to get information about the device.

       --detail-platform
	      Print detail of the platform's RAID capabilities (firmware / hardware topology).	If the metadata is specified with  -e  or  --meta-
	      data= then the return status will be:

	      0      metadata successfully enumerated its platform components on this system

	      1      metadata is platform independent

	      2      metadata failed to find its platform components on this system

       --update-subarray=
	      If the device is a container and the argument to --update-subarray specifies a subarray in the container, then attempt to update the
	      given superblock field in the subarray.  Similar to updating an array in "assemble" mode, the field to update is selected by  -U	or
	      --update= option. The supported options are name, ppl and no-ppl.

	      The  name  option updates the subarray name in the metadata, it may not affect the device node name or the device node symlink until
	      the subarray is re-assembled.  If updating name would change the UUID of an active subarray this operation is blocked, and the  com-
	      mand will end in an error.

	      The ppl and no-ppl options enable and disable PPL in the metadata. Currently supported only for IMSM subarrays.

       --examine
	      The  device  should  be  a  component of an md array.  mdadm will read the md superblock of the device and display the contents.	If
	      --brief or --scan is given, then multiple devices that are components of the one array are grouped together and reported in a single
	      entry suitable for inclusion in mdadm.conf.

	      Having --scan without listing any devices will cause all devices listed in the config file to be examined.

       --dump=directory
	      If the device contains RAID metadata, a file will be created in the directory and the metadata will be written to it.  The file will
	      be the same size as the device and have the metadata written in the file at the same locate that it exists in the  device.   However
	      the file will be "sparse" so that only those blocks containing metadata will be allocated. The total space used will be small.

	      The  file  name  used  in  the directory will be the base name of the device.   Further if any links appear in /dev/disk/by-id which
	      point to the device, then hard links to the file will be created in directory based on these by-id names.

	      Multiple devices can be listed and their metadata will all be stored in the one directory.

       --restore=directory
	      This is the reverse of --dump.  mdadm will locate a file in the directory that has a name appropriate for the given device and  will
	      restore  metadata  from it.  Names that match /dev/disk/by-id names are preferred, however if two of those refer to different files,
	      mdadm will not choose between them but will abort the operation.

	      If a file name is given instead of a directory then mdadm will restore from that file to a single device, always provided  the  size
	      of the file matches that of the device, and the file contains valid metadata.

       --stop The devices should be active md arrays which will be deactivated, as long as they are not currently in use.

       --run  This will fully activate a partially assembled md array.

       --readonly
	      This will mark an active array as read-only, providing that it is not currently being used.

       --readwrite
	      This will change a readonly array back to being read/write.

       --scan For  all	operations  except  --examine,	--scan	will  cause the operation to be applied to all arrays listed in /proc/mdstat.  For
	      --examine, --scan causes all devices listed in the config file to be examined.

       -b, --brief
	      Be less verbose.	This is used with --detail and --examine.  Using --brief with --verbose gives an intermediate level of verbosity.

MONITOR MODE
       Usage: mdadm --monitor options... devices...

       This usage causes mdadm to periodically poll a number of md arrays and to report on any events noticed.	mdadm  will  never  exit  once	it
       decides that there are arrays to be checked, so it should normally be run in the background.

       As  well  as  reporting events, mdadm may move a spare drive from one array to another if they are in the same spare-group or domain and if
       the destination array has a failed drive but no spares.

       If any devices are listed on the command line, mdadm will only monitor those devices.  Otherwise all arrays  listed  in	the  configuration
       file will be monitored.	Further, if --scan is given, then any other md devices that appear in /proc/mdstat will also be monitored.

       The  result  of monitoring the arrays is the generation of events.  These events are passed to a separate program (if specified) and may be
       mailed to a given E-mail address.

       When passing events to a program, the program is run once for each event, and is given 2 or 3 command-line arguments: the first is the name
       of the event (see below), the second is the name of the md device which is affected, and the third is the name of a related device if rele-
       vant (such as a component device that has failed).

       If --scan is given, then a program or an E-mail address must be specified on the command line or in the config file.  If neither are avail-
       able,  then mdadm will not monitor anything.  Without --scan, mdadm will continue monitoring as long as something was found to monitor.	If
       no program or email is given, then each event is reported to stdout.

       The different events are:

	   DeviceDisappeared
		  An md array which previously was configured appears to no longer be configured. (syslog priority: Critical)

		  If mdadm was told to monitor an array which is RAID0 or Linear, then it will report DeviceDisappeared with the extra information
		  Wrong-Level.	This is because RAID0 and Linear do not support the device-failed, hot-spare and resync operations which are moni-
		  tored.

	   RebuildStarted
		  An md array started reconstruction (e.g. recovery, resync, reshape, check, repair). (syslog priority: Warning)

	   RebuildNN
		  Where NN is a two-digit number (ie. 05, 48). This indicates that rebuild has passed that many percent of the total.  The  events
		  are  generated  with fixed increment since 0. Increment size may be specified with a commandline option (default is 20). (syslog
		  priority: Warning)

	   RebuildFinished
		  An md array that was rebuilding, isn't any more, either because it finished normally or was aborted. (syslog priority: Warning)

	   Fail   An active component device of an array has been marked as faulty. (syslog priority: Critical)

	   FailSpare
		  A spare component device which was being rebuilt to replace a faulty device has failed. (syslog priority: Critical)

	   SpareActive
		  A spare component device which was being rebuilt to replace a faulty device has been successfully  rebuilt  and  has	been  made
		  active.  (syslog priority: Info)

	   NewArray
		  A new md array has been detected in the /proc/mdstat file.  (syslog priority: Info)

	   DegradedArray
		  A  newly  noticed  array  appears to be degraded.  This message is not generated when mdadm notices a drive failure which causes
		  degradation, but only when mdadm notices that an array is degraded when it first sees the array.  (syslog priority: Critical)

	   MoveSpare
		  A spare drive has been moved from one array in a spare-group or domain to another to allow a failed drive to be replaced.  (sys-
		  log priority: Info)

	   SparesMissing
		  If mdadm has been told, via the config file, that an array should have a certain number of spare devices, and mdadm detects that
		  it has fewer than this number when it first sees the array, it will report a SparesMissing message.  (syslog priority: Warning)

	   TestMessage
		  An array was found at startup, and the --test flag was given.  (syslog priority: Info)

       Only Fail, FailSpare, DegradedArray, SparesMissing and TestMessage cause Email to be sent.  All events cause the program to  be	run.   The
       program is run with two or three arguments: the event name, the array device and possibly a second device.

       Each  event  has an associated array device (e.g.  /dev/md1) and possibly a second device.  For Fail, FailSpare, and SpareActive the second
       device is the relevant component device.  For MoveSpare the second device is the array that the spare was moved from.

       For mdadm to move spares from one array to another, the different arrays need to be labeled with the same spare-group or the spares must be
       allowed to migrate through matching POLICY domains in the configuration file.  The spare-group name can be any string; it is only necessary
       that different spare groups use different names.

       When mdadm detects that an array in a spare group has fewer active devices than necessary for the complete array, and has no spare devices,
       it  will  look  for another array in the same spare group that has a full complement of working drive and a spare.  It will then attempt to
       remove the spare from the second drive and add it to the first.	If the removal succeeds but the adding fails, then it is added back to the
       original array.

       If  the	spare  group  for  a  degraded	array is not defined, mdadm will look at the rules of spare migration specified by POLICY lines in
       mdadm.conf and then follow similar steps as above if a matching spare is found.

GROW MODE
       The GROW mode is used for changing the size or shape of an active array.  For this to work, the kernel must support the	necessary  change.
       Various types of growth are being added during 2.6 development.

       Currently the supported changes include

       o   change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.

       o   increase or decrease the "raid-devices" attribute of RAID0, RAID1, RAID4, RAID5, and RAID6.

       o   change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.

       o   convert  between RAID1 and RAID5, between RAID5 and RAID6, between RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2
	   mode).

       o   add a write-intent bitmap to any array which supports these bitmaps, or remove a write-intent bitmap from such an array.

       o   change the array's consistency policy.

       Using GROW on containers is currently supported only for Intel's IMSM container format.	The number  of	devices  in  a	container  can	be
       increased  -  which affects all arrays in the container - or an array in a container can be converted between levels where those levels are
       supported by the container, and the conversion is on of those listed above.  Resizing arrays in an IMSM container with --grow --size is not
       yet supported.

       Notes:

       o   Intel's native checkpointing doesn't use --backup-file option and it is transparent for assembly feature.

       o   Roaming between Windows(R) and Linux systems for IMSM metadata is not supported during grow process.

   SIZE CHANGES
       Normally  when  an  array is built the "size" is taken from the smallest of the drives.	If all the small drives in an arrays are, one at a
       time, removed and replaced with larger drives, then you could have an array of large drives with only a small amount used.  In this  situa-
       tion,  changing	the  "size"  with  "GROW"  mode  will  allow the extra space to start being used.  If the size is increased in this way, a
       "resync" process will start to make sure the new parts of the array are synchronised.

       Note that when an array changes size, any filesystem that may be stored in the array will not automatically grow or shrink to use or vacate
       the  space.   The filesystem will need to be explicitly told to use the extra space after growing, or to reduce its size prior to shrinking
       the array.

       Also the size of an array cannot be changed while it has an active bitmap.  If an array has a bitmap, it must be removed  before  the  size
       can be changed. Once the change is complete a new bitmap can be created.

       Note: --grow --size is not yet supported for external file bitmap.

   RAID-DEVICES CHANGES
       A  RAID1  array	can  work  with  any number of devices from 1 upwards (though 1 is not very useful).  There may be times which you want to
       increase or decrease the number of active devices.  Note that this is different to hot-add or hot-remove which changes the number of  inac-
       tive devices.

       When  reducing  the  number of devices in a RAID1 array, the slots which are to be removed from the array must already be vacant.  That is,
       the devices which were in those slots must be failed and removed.

       When the number of devices is increased, any hot spares that are present will be activated immediately.

       Changing the number of active devices in a RAID5 or RAID6 is much more effort.  Every block in the array will need to be read  and  written
       back to a new location.	From 2.6.17, the Linux Kernel is able to increase the number of devices in a RAID5 safely, including restarting an
       interrupted "reshape".  From 2.6.31, the Linux Kernel is able to increase or decrease the number of devices in a RAID5 or RAID6.

       From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4 or RAID5.  mdadm uses this functionality	and  the  ability  to  add
       devices	to  a  RAID4 to allow devices to be added to a RAID0.  When requested to do this, mdadm will convert the RAID0 to a RAID4, add the
       necessary disks and make the reshape happen, and then convert the RAID4 back to RAID0.

       When decreasing the number of devices, the size of the array will also decrease.  If there was data in the array, it  could  get  destroyed
       and  this  is  not  reversible, so you should firstly shrink the filesystem on the array to fit within the new size.  To help prevent acci-
       dents, mdadm requires that the size of the array be decreased first with mdadm --grow --array-size.  This is a reversible change which sim-
       ply makes the end of the array inaccessible.  The integrity of any data can then be checked before the non-reversible reduction in the num-
       ber of devices is request.

       When relocating the first few stripes on a RAID5 or RAID6, it is not possible to keep the data on disk  completely  consistent  and  crash-
       proof.  To provide the required safety, mdadm disables writes to the array while this "critical section" is reshaped, and takes a backup of
       the data that is in that section.  For grows, this backup may be stored in any spare devices that the array has, however  it  can  also	be
       stored in a separate file specified with the --backup-file option, and is required to be specified for shrinks, RAID level changes and lay-
       out changes.  If this option is used, and the system does crash during the critical period, the same file must be passed to  --assemble	to
       restore	the  backup  and reassemble the array.	When shrinking rather than growing the array, the reshape is done from the end towards the
       beginning, so the "critical section" is at the end of the reshape.

   LEVEL CHANGES
       Changing the RAID level of any array happens instantaneously.  However in the RAID5 to RAID6 case this requires a  non-standard	layout	of
       the  RAID6  data,  and in the RAID6 to RAID5 case that non-standard layout is required before the change can be accomplished.  So while the
       level change is instant, the accompanying layout change can take quite a long time.  A --backup-file is required.   If  the  array  is  not
       simultaneously  being  grown or shrunk, so that the array size will remain the same - for example, reshaping a 3-drive RAID5 into a 4-drive
       RAID6 - the backup file will be used not just for a "cricital section" but throughout the reshape operation, as described below under  LAY-
       OUT CHANGES.

   CHUNK-SIZE AND LAYOUT CHANGES
       Changing the chunk-size of layout without also changing the number of devices as the same time will involve re-writing all blocks in-place.
       To ensure against data loss in the case of a crash, a --backup-file must be provided for these changes.	Small sections of the  array  will
       be copied to the backup file while they are being rearranged.  This means that all the data is copied twice, once to the backup and once to
       the new layout on the array, so this type of reshape will go very slowly.

       If the reshape is interrupted for any reason, this backup file must be made available to mdadm --assemble so the array can be  reassembled.
       Consequently the file cannot be stored on the device being reshaped.

   BITMAP CHANGES
       A  write-intent	bitmap	can be added to, or removed from, an active array.  Either internal bitmaps, or bitmaps stored in a separate file,
       can be added.  Note that if you add a bitmap stored in a file which is in a filesystem that is on the RAID array being affected, the system
       will deadlock.  The bitmap must be on a separate filesystem.

   CONSISTENCY POLICY CHANGES
       The  consistency  policy of an active array can be changed by using the --consistency-policy option in Grow mode. Currently this works only
       for the ppl and resync policies and allows to enable or disable the RAID5 Partial Parity Log (PPL).

INCREMENTAL MODE
       Usage: mdadm --incremental [--run] [--quiet] component-device [optional-aliases-for-device]

       Usage: mdadm --incremental --fail component-device

       Usage: mdadm --incremental --rebuild-map

       Usage: mdadm --incremental --run --scan

       This mode is designed to be used in conjunction with a device discovery system.	As devices are found in a system, they can  be	passed	to
       mdadm --incremental to be conditionally added to an appropriate array.

       Conversely,  it	can  also  be used with the --fail flag to do just the opposite and find whatever array a particular device is part of and
       remove the device from that array.

       If the device passed is a CONTAINER device created by a previous call to mdadm, then rather than trying to add that device to an array, all
       the arrays described by the metadata of the container will be started.

       mdadm  performs	a number of tests to determine if the device is part of an array, and which array it should be part of.  If an appropriate
       array is found, or can be created, mdadm adds the device to the array and conditionally starts the array.

       Note that mdadm will normally only add devices to an array which were previously working (active or spare) parts of that array.	 The  sup-
       port for automatic inclusion of a new drive as a spare in some array requires a configuration through POLICY in config file.

       The tests that mdadm makes are as follow:

       +      Is the device permitted by mdadm.conf?  That is, is it listed in a DEVICES line in that file.  If DEVICES is absent then the default
	      it to allow any device.  Similarly if DEVICES contains the special word partitions then any device is allowed.  Otherwise the device
	      name  given to mdadm, or one of the aliases given, or an alias found in the filesystem, must match one of the names or patterns in a
	      DEVICES line.

	      This is the only context where the aliases are used.  They are usually provided by a udev rules mentioning $env{DEVLINKS}.

       +      Does the device have a valid md superblock?  If a specific metadata version is requested with --metadata or -e then only that  style
	      of  metadata  is accepted, otherwise mdadm finds any known version of metadata.  If no md metadata is found, the device may be still
	      added to an array as a spare if POLICY allows.

       mdadm keeps a list of arrays that it has partially assembled in /run/mdadm/map.	If no array exists which matches the metadata on  the  new
       device, mdadm must choose a device name and unit number.  It does this based on any name given in mdadm.conf or any name information stored
       in the metadata.  If this name suggests a unit number, that number will be used, otherwise a free unit number  will  be	chosen.   Normally
       mdadm will prefer to create a partitionable array, however if the CREATE line in mdadm.conf suggests that a non-partitionable array is pre-
       ferred, that will be honoured.

       If the array is not found in the config file and its metadata does not identify it as belonging to the "homehost", then mdadm will choose a
       name  for  the  array which is certain not to conflict with any array which does belong to this host.  It does this be adding an underscore
       and a small number to the name preferred by the metadata.

       Once an appropriate array is found or created and the device is added, mdadm must decide if the array is ready to be started.  It will nor-
       mally  compare the number of available (non-spare) devices to the number of devices that the metadata suggests need to be active.  If there
       are at least that many, the array will be started.  This means that if any devices are missing the array will not be restarted.

       As an alternative, --run may be passed to mdadm in which case the array will be run as soon as there are enough	devices  present  for  the
       data  to  be accessible.  For a RAID1, that means one device will start the array.  For a clean RAID5, the array will be started as soon as
       all but one drive is present.

       Note that neither of these approaches is really ideal.  If it can be known that all device discovery has completed, then
	  mdadm -IRs
       can be run which will try to start all arrays that are being incrementally assembled.  They are started in "read-auto" mode in  which  they
       are  read-only  until  the first write request.	This means that no metadata updates are made and no attempt at resync or recovery happens.
       Further devices that are found before the first write can still be added safely.

ENVIRONMENT
       This section describes environment variables that affect how mdadm operates.

       MDADM_NO_MDMON
	      Setting this value to 1 will prevent mdadm from automatically launching mdmon.  This variable is intended  primarily  for  debugging
	      mdadm/mdmon.

       MDADM_NO_UDEV
	      Normally, mdadm does not create any device nodes in /dev, but leaves that task to udev.  If udev appears not to be configured, or if
	      this environment variable is set to '1', the mdadm will create and devices that are needed.

       MDADM_NO_SYSTEMCTL
	      If mdadm detects that systemd is in use it will normally request systemd to start  various  background  tasks  (particularly  mdmon)
	      rather than forking and running them in the background.  This can be suppressed by setting MDADM_NO_SYSTEMCTL=1.

       IMSM_NO_PLATFORM
	      A  key  value  of IMSM metadata is that it allows interoperability with boot ROMs on Intel platforms, and with other major operating
	      systems.	Consequently, mdadm will only allow an IMSM array to be created or modified if detects that it	is  running  on  an  Intel
	      platform which supports IMSM, and supports the particular configuration of IMSM that is being requested (some functionality requires
	      newer OROM support).

	      These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the environment.	This can be useful for	testing  or  for  disaster
	      recovery.  You should be aware that interoperability may be compromised by setting this value.

       MDADM_GROW_ALLOW_OLD
	      If an array is stopped while it is performing a reshape and that reshape was making use of a backup file, then when the array is re-
	      assembled mdadm will sometimes complain that the backup file is too old.	If this happens and you are certain it is the right backup
	      file, you can over-ride this check by setting MDADM_GROW_ALLOW_OLD=1 in the environment.

       MDADM_CONF_AUTO
	      Any  string  given  in this variable is added to the start of the AUTO line in the config file, or treated as the whole AUTO line if
	      none is given.  It can be used to disable certain metadata types when mdadm is called from a boot script.  For example
		  export MDADM_CONF_AUTO='-ddf -imsm'
	      will make sure that mdadm does not automatically assemble any DDF or IMSM arrays that are found.	This can be useful on systems con-
	      figured to manage such arrays with dmraid.

EXAMPLES
	 mdadm --query /dev/name-of-device
       This will find out if a given device is a RAID array, or is part of one, and will provide brief information about the device.

	 mdadm --assemble --scan
       This will assemble and start all arrays listed in the standard config file.  This command will typically go in a system startup file.

	 mdadm --stop --scan
       This will shut down all arrays that can be shut down (i.e. are not currently in use).  This will typically go in a system shutdown script.

	 mdadm --follow --scan --delay=120
       If  (and  only  if) there is an Email address or program given in the standard config file, then monitor the status of all arrays listed in
       that file by polling them ever 2 minutes.

	 mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1
       Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.

	 echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf
	 mdadm --detail --scan >> mdadm.conf
       This will create a prototype config file that describes currently active arrays that are known to be made from partitions of  IDE  or  SCSI
       drives.	This file should be reviewed before being used as it may contain unwanted detail.

	 echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf
	 mdadm --examine --scan --config=mdadm.conf >> mdadm.conf
       This  will  find arrays which could be assembled from existing IDE and SCSI whole drives (not partitions), and store the information in the
       format of a config file.  This file is very likely to contain unwanted detail, particularly the devices= entries.  It  should  be  reviewed
       and edited before being used as an actual config file.

	 mdadm --examine --brief --scan --config=partitions
	 mdadm -Ebsc partitions
       Create a list of devices by reading /proc/partitions, scan these for RAID superblocks, and printout a brief listing of all that were found.

	 mdadm -Ac partitions -m 0 /dev/md0
       Scan  all  partitions  and  devices  listed in /proc/partitions and assemble /dev/md0 out of all such devices with a RAID superblock with a
       minor number of 0.

	 mdadm --monitor --scan --daemonise > /run/mdadm/mon.pid
       If config file contains a mail address or alert program, run mdadm in the background in monitor mode monitoring all md devices.	Also write
       pid of mdadm daemon to /run/mdadm/mon.pid.

	 mdadm -Iq /dev/somedevice
       Try to incorporate newly discovered device into some array as appropriate.

	 mdadm --incremental --rebuild-map --run --scan
       Rebuild the array map from any current arrays, and then start any that can be started.

	 mdadm /dev/md4 --fail detached --remove detached
       Any devices which are components of /dev/md4 will be marked as faulty and then remove from the array.

	 mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
       The array /dev/md4 which is currently a RAID5 array will be converted to RAID6.	There should normally already be a spare drive attached to
       the array as a RAID6 needs one more drive than a matching RAID5.

	 mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]
       Create a DDF array over 6 devices.

	 mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf
       Create a RAID5 array over any 3 devices in the given DDF set.  Use only 30 gigabytes of each device.

	 mdadm -A /dev/md/ddf1 /dev/sd[a-f]
       Assemble a pre-exist ddf array.

	 mdadm -I /dev/md/ddf1
       Assemble all arrays contained in the ddf array, assigning names as appropriate.

	 mdadm --create --help
       Provide help about the Create mode.

	 mdadm --config --help
       Provide help about the format of the config file.

	 mdadm --help
       Provide general help.

FILES
   /proc/mdstat
       If you're using the /proc filesystem, /proc/mdstat lists all active md devices with information about them.  mdadm uses this to find arrays
       when --scan is given in Misc mode, and to monitor array reconstruction on Monitor mode.

   /etc/mdadm/mdadm.conf (or /etc/mdadm.conf)
       The  config  file  lists  which devices may be scanned to see if they contain MD super block, and gives identifying information (e.g. UUID)
       about known MD arrays.  See mdadm.conf(5) for more details.

   /etc/mdadm/mdadm.conf.d (or /etc/mdadm.conf.d)
       A directory containing configuration files which are read in lexical order.

   /run/mdadm/map
       When --incremental mode is used, this file gets a list of arrays currently being created.

DEVICE NAMES
       mdadm understand two sorts of names for array devices.

       The first is the so-called 'standard' format name, which matches the names used by the kernel and which appear in /proc/mdstat.

       The second sort can be freely chosen, but must reside in /dev/md/.  When giving a device name to mdadm to  create  or  assemble	an  array,
       either  full  path  name  such as /dev/md0 or /dev/md/home can be given, or just the suffix of the second sort of name, such as home can be
       given.

       When mdadm chooses device names during auto-assembly or incremental assembly, it will sometimes add a small sequence number to the  end	of
       the  name  to avoid conflicted between multiple arrays that have the same name.	If mdadm can reasonably determine that the array really is
       meant for this host, either by a hostname in the metadata, or by the presence of the array in mdadm.conf, then it will leave off the suffix
       if  possible.   Also  if  the  homehost is specified as <ignore> mdadm will only use a suffix if a different array of the same name already
       exists or is listed in the config file.

       The standard names for non-partitioned arrays (the only sort of md array available in 2.4 and earlier) are of the form

	      /dev/mdNN

       where NN is a number.  The standard names for partitionable arrays (as available from 2.6 onwards) are of the form:

	      /dev/md_dNN

       Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".

       From kernel version 2.6.28 the "non-partitioned array" can actually be partitioned.  So the "md_dNN" names are no longer needed, and parti-
       tions such as "/dev/mdNNpXX" are possible.

       From kernel version 2.6.29 standard names can be non-numeric following the form:

	      /dev/md_XXX

       where XXX is any string.  These names are supported by mdadm since version 3.3 provided they are enabled in mdadm.conf.

NOTE
       mdadm was previously known as mdctl.

SEE ALSO
       For further information on mdadm usage, MD and the various levels of RAID, see:

	      http://raid.wiki.kernel.org/

       (based upon Jakob Ostergaard's Software-RAID.HOWTO)

       The latest version of mdadm should always be available from

	      http://www.kernel.org/pub/linux/utils/raid/mdadm/

       Related man pages:

       mdmon(8), mdadm.conf(5), md(4).

v4.1-rc1																  MDADM(8)

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