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MDADM(8)										 MDADM(8)

       mdadm - manage MD devices aka Linux Software Raid.

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

       RAID  devices are virtual devices created from two or more real block devices. This allows
       multiple devices (typically disk drives or partitions there-of) to be combined into a sin-
       gle 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

       Currently,  Linux  supports  LINEAR md devices, RAID0 (striping), RAID1 (mirroring), RAID4
       and RAID5.

       Recent kernels (2002) also support a mode known as MULTIPATH.  mdadm only provides limited
       support for MULTIPATH as yet.

       mdadm is a program that can be used to create, manage, and monitor MD devices.  As such it
       provides a similar set of functionality to the raidtools packages.   The  key  differences
       between mdadm and raidtools are:

       o   mdadm is a single program and not a collection of programs.

       o   mdadm  can  perform (almost) all of its functions without having a configuration file.
	   Also mdadm helps with management of the configuration file.

       o   mdadm can provide information about your arrays (through Query, Detail,  and  Examine)
	   that raidtools cannot.

       mdadm has 6 major modes of operation:

	      Assemble	the  parts 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 assemble a faulty array.

       Build  Build a legacy array without per-device superblocks.

       Create Create a new array with per-device superblocks.

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

       Misc   This  mode allows operations on independent devices such as examine MD superblocks,
	      erasing old superblocks and stopping active arrays.

       Follow or Monitor
	      Monitor one or more md devices and act on any state changes.

       Available options are:

       -A, --assemble
	      Assemble a pre-existing array.

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

       -C, --create
	      Create a new array.

       -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 detail of one or more md devices.

       -E, --examine
	      Print content of md superblock on device(s).

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

       -h, --help
	      Display help message or, after above option, mode specific help message.

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

       -v, --verbose
	      Be more verbose about what is happening.

       -b, --brief
	      Be less verbose.	This is used with --detail and --examine.

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

       -c, --config=
	      Specify the config file.	Default is /etc/mdadm.conf.

       -s, --scan
	      scan config file or /proc/mdstat for missing information.  In general, this  option
	      gives  mdadm  permission	to  get  any missing information, like component devices,
	      array devices, array identities, and alert destination from the configuration file:
	      /etc/mdadm.conf.	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.

For create or build:
       -c, --chunk=
	      Specify chunk size of kibibytes.	The default is 64.

	      Specify rounding factor for linear array (==chunk size)

       -l, --level=
	      Set raid level.  Options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid5, 4,
	      raid5, 5, multipath, mp.	Obviously some of these are synonymous.  Only the first 4
	      are valid when Building.

       -p, --parity=
	      Set raid5 parity algorithm. Options are:	left-asymmetric,  left-symmetric,  right-
	      asymmetric, right-symmetric, la, ra, ls, rs.  The default is left-symmetric.

	      same as --parity

       -n, --raid-devices=
	      number of active devices in array.

       -x, --spare-devices=
	      number  of spare (eXtra) devices in initial array.  Spares can be added and removed

       -z, --size=
	      Amount (in Kibibytes) of space to use from each drive in RAID1/4/5.  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.

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.

       -f, --force
	      Assemble the array even if some superblocks appear out-of-date

       -R, --run
	      Attempt  to  start  the array even if fewer drives were given than are needed for a
	      full array. Normally if not all 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.

For Manage mode:
       -a, --add
	      hotadd listed devices.

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

       -f, --fail
	      mark listed devices as faulty.

	      same as --fail.

For Misc mode:
       -R, --run
	      start a partially built array.

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

       -o, --readonly
	      mark array as readonly.

       -w, --readwrite
	      mark array as readwrite.

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

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.

       -d, --delay
	      Give  a  delay in seconds.  mdadm polls the md arrays and then waits this many sec-
	      onds before polling again.  The default is 60 seconds.

       Usage: mdadm --assemble device 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 com-
       ponent-devices. These can be found in a number of ways.

       The md device is either given before --scan or is found from the config file. In the  lat-
       ter case, multiple md devices can be started with a single mdadm command.

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

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

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

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

       Normally  the array will be started after it is assembled.  However if --scan is not given
       and insufficient drives were listed to start a complete	(non-degraded)	array,	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 or RAID5), give the --run flag.

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

       This usage is similar to --create.  The difference is that it creates a legacy array with-
       out  a superblock. With these arrays there is no difference 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 only be 0, raid0, or linear. All devices must be listed and the array will
       be started once complete.

       Usage: mdadm --create 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.

       As devices are added, they are checked to see if they contain raid superblocks or filesys-
       tems. They are also checked to see if the variance 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 miss-
       ing 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 RAID1
       array, only one real device needs to be given.  All of the others can be missing.

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

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

	      start the array readonly - not supported yet.

       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.

       Usage: mdadm options ...  devices ...

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

	      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.

	      The  device  should be an active md device.  mdadm will display a detailed descrip-
	      tion of the array.  --brief or --scan will cause the output to be less detailed and
	      the format to be suitable for inclusion in /etc/mdadm.conf.

	      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 is given, or --scan then multi-
	      ple  devices that are components of the one array are grouped together and reported
	      in a single entry suitable for inclusion in /etc/mdadm.conf.

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

       --stop This  devices  should  active  md arrays which will be deactivated, if they are not
	      currently in use.

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

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

	      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.

       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 and if the destination array has a failed drive  but  not

       If any devices are listed on the command line, mdadm will only monitor those devices. Oth-
       erwise 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 event to program, the program is run once for each event and is given 2 or	3
       command-line  arguements.   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 relevant, 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 available, then mdadm will  not  monitor  any-
       thing.	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:

		  An md array which previously was configured appears to no longer be configured.

		  An md array started reconstruction.

		  Where NN is 20, 40, 60, or 80, this indicates that rebuild has passed that many
		  percentage of the total.

	   Fail   An active component device of an array has been marked as faulty.

		  A spare component device which was being rebuilt to replace a faulty device has

		  A spare component device which was being rebuilt to replace a faulty device  as
		  been successfully rebuild and has been made active.

		  A new md array has been detected in the /proc/mdstat file.

		  A  spare  drive  has	been  moved from one array in a spare-group to another to
		  allow a failed drive to be replaced.

       Only Fail and FailSpare cause Email to be sent.	All events cause the program to  be  run.
       The  program  is  run  with  two  or three arguments, they being 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
       labelled with the same spare-group 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 which is 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.

       To find out if a devices is a raid array or part of one:
	 mdadm -Q /dev/name-of-device

       To assemble and start all array listed in the standard config file:
	 mdadm -As

       To shut down all arrays (that are not still in used):
	 mdadm --stop --scan

       To monitor all arrays if (and only if) an email address or program was given in the config
       file, but poll every 2 minutes:
	 mdadm -Fs --delay=120

       To create /dev/md0 as a RAID1 array with /dev/hda1 and /dev/hdc1:
	 mdadm -C /dev/md0 -l1 -n2 /dev/hd[ac]1

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

       To find out what raid arrays could be assembled from existing IDE and  SCSI  whole  drives
       (not partitions):
	 echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf
	  mdadm  -Es  -c  mdadm.conf  >>  mdadm.conf This file is very likely to contain unwanted
       detail, particularly the devices= entries.

       To get help about Create mode:
	 mdadm --create --help

       To get help about the format of the config file:
	 mdadm --config --help

       To get general help:
	 mdadm --help

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

       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.

       mdadm was previously known as mdctl.

       For information on the various levels of RAID, check out:


       for new releases of the RAID driver check out:




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

       raidtab(5), raid0run(8), raidstop(8), mkraid(8)

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