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Linux 2.6 - man page for mdadm.conf (linux section 5)

MDADM.CONF(5)									    MDADM.CONF(5)

       mdadm.conf - configuration for management of Software RAID with mdadm


       mdadm is a tool for creating, managing, and monitoring RAID devices using the md driver in

       Some common tasks, such as assembling all arrays, can  be  simplified  by  describing  the
       devices and arrays in this configuration file.

       The  file should be seen as a collection of words separated by white space (space, tab, or
       newline).  Any word that beings with a hash sign  (#)  starts  a  comment  and  that  word
       together with the remainder of the line is ignored.

       Any  line  that starts with white space (space or tab) is treated as though it were a con-
       tinuation of the previous line.

       Empty lines are ignored, but otherwise each (non continuation) line must start with a key-
       word as listed below.  The keywords are case insensitive and can be abbreviated to 3 char-

       The keywords are:

       DEVICE A device line lists the devices (whole devices or partitions) that might contain	a
	      component  of an MD array.  When looking for the components of an array, mdadm will
	      scan these devices (or any devices listed on the command line).

	      The device line may contain a number of different devices (separated by spaces) and
	      each device name can contain wild cards as defined by glob(7).

	      Also, there may be several device lines present in the file.

	      Alternatively,  a  device  line can contain either of both of the  words containers
	      and partitions.  The word containers will cause mdadm to look  for  assembled  CON-
	      TAINER arrays and included them as a source for assembling further arrays.

	      The  word  partitions  will  cause  mdadm  to read /proc/partitions and include all
	      devices and partitions found therein.  mdadm does not use the names from /proc/par-
	      titions  but  only  the  major and minor device numbers.	It scans /dev to find the
	      name that matches the numbers.

	      If no DEVICE line is present, then "DEVICE partitions containers" is assumed.

	      For example:

	      DEVICE /dev/hda* /dev/hdc*
	      DEV    /dev/sd*
	      DEVICE /dev/disk/by-path/pci*
	      DEVICE partitions

       ARRAY  The ARRAY lines identify actual arrays.  The second word on the  line  may  be  the
	      name  of	the  device  where  the  array is normally assembled, such as /dev/md1 or
	      /dev/md/backup.  If the name does not start with a slash ('/'), it  is  treated  as
	      being  in  /dev/md/.   Alternately the word <ignore> (complete with angle brackets)
	      can be given in which case any array which matches the rest of the line will  never
	      be  automatically  assembled.   If  no device name is given, mdadm will use various
	      heuristics to determine an appropriate name.

	      Subsequent words identify the array, or identify the array as a member of a  group.
	      If multiple identities are given, then a component device must match ALL identities
	      to be considered a match.  Each identity word has a tag, and equals sign, and  some
	      value.  The tags are:

	   uuid=  The  value  should  be  a  128 bit uuid in hexadecimal, with punctuation inter-
		  spersed if desired.  This must match the uuid stored in the superblock.

	   name=  The value should be a simple textual name as was given to mdadm when the  array
		  was created.	This must match the name stored in the superblock on a device for
		  that device to be included in the array.  Not all  superblock  formats  support

		  The value is an integer which indicates the minor number that was stored in the
		  superblock when the array was created. When an array is  created  as	/dev/mdX,
		  then the minor number X is stored.

		  The  value  is  a comma separated list of device names or device name patterns.
		  Only devices with names which match one entry in  the  list  will  be  used  to
		  assemble  the array.	Note that the devices listed there must also be listed on
		  a DEVICE line.

	   level= The value is a raid level.  This is not normally used to identify an array, but
		  is supported so that the output of

		  mdadm --examine --scan

		  can be use directly in the configuration file.

		  The  value is the number of devices in a complete active array.  As with level=
		  this is mainly for compatibility with the output of

		  mdadm --examine --scan.

		  The value is a number of spare devices to expect the array to have.	The  sole
		  use  of  this  keyword  and value is as follows: mdadm --monitor will report an
		  array if it is found to have fewer than this number of  spares  when	--monitor
		  starts or when --oneshot is used.

		  The  value  is  a textual name for a group of arrays.  All arrays with the same
		  spare-group name are considered to be part of the same group.  The significance
		  of  a  group	of  arrays is that mdadm will, when monitoring the arrays, move a
		  spare drive from one array in a group to another array in  that  group  if  the
		  first array had a failed or missing drive but no spare.

	   auto=  This option is rarely needed with mdadm-3.0, particularly if use with the Linux
		  kernel v2.6.28 or later.  It tells mdadm whether to use partitionable array  or
		  non-partitionable  arrays  and,  in  the  absence  of  udev, how many partition
		  devices to create.  From 2.6.28 all md array devices are  partitionable,  hence
		  this option is not needed.

		  The  value  of this option can be "yes" or "md" to indicate that a traditional,
		  non-partitionable md array should be created, or "mdp", "part"  or  "partition"
		  to  indicate	that  a  partitionable	md array (only available in linux 2.6 and
		  later) should be used.  This later set can also have a number appended to indi-
		  cate	how  many  partitions  to  create device files for, e.g.  auto=mdp5.  The
		  default is 4.

		  The option specifies a file in which a write-intent  bitmap  should  be  found.
		  When assembling the array, mdadm will provide this file to the md driver as the
		  bitmap file.	This has  the  same  function  as  the	--bitmap-file  option  to

		  Specify  the metadata format that the array has.  This is mainly recognised for
		  comparability with the output of mdadm -Es.

		  Specify that this array is a member array of some container.	The  value  given
		  can be either a path name in /dev, or a UUID of the container array.

		  Specify that this array is a member array of some container.	Each type of con-
		  tainer has some way to enumerate member arrays, often a simple sequence number.
		  The value identifies which member of a container the array is.  It will usually
		  accompany a "container=" word.

	      The mailaddr line gives an E-mail address that alerts should be sent to when  mdadm
	      is  running in --monitor mode (and was given the --scan option).	There should only
	      be one MAILADDR line and it should have only one address.

	      The mailfrom line (which can only be abbreviated to at least 5 characters) gives an
	      address to appear in the "From" address for alert mails.	This can be useful if you
	      want to explicitly set a domain, as the default from  address  is  "root"  with  no
	      domain.  All words on this line are catenated with spaces to form the address.

	      Note  that this value cannot be set via the mdadm commandline.  It is only settable
	      via the config file.

	      The program line gives the name of a program to be run when mdadm --monitor detects
	      potentially  interesting	events	on any of the arrays that it is monitoring.  This
	      program gets run with two or three arguments, they being the Event, the md  device,
	      and possibly the related component device.

	      There should only be one program line and it should be give only one program.

       CREATE The  create  line  gives	default values to be used when creating arrays and device
	      entries for arrays.  These include:


	   group= These can give user/group ids or  names  to  use  instead  of  system  defaults
		  (root/wheel or root/disk).

	   mode=  An octal file mode such as 0660 can be given to override the default of 0600.

	   auto=  This	corresponds to the --auto flag to mdadm.  Give yes, md, mdp, part -- pos-
		  sibly followed by a number of partitions --  to  indicate  how  missing  device
		  entries should be created.

		  The  name  of the metadata format to use if none is explicitly given.  This can
		  be useful to impose a system-wide default of version-1 superblocks.

		  Normally when creating devices in /dev/md/ mdadm will create a matching symlink
		  from	/dev/  with a name starting md or md_.	Give symlinks=no to suppress this
		  symlink creation.

	      The homehost line gives a default value for the --homehost= option to mdadm.  There
	      should  normally	be  only  one other word on the line.  It should either be a host
	      name, or one of the special words <system> and <ignore>.	 If  <system>  is  given,
	      then the gethostname(2) systemcall is used to get the host name.

	      If  <ignore> is given, then a flag is set so that when arrays are being auto-assem-
	      bled the checking of the recorded homehost is disabled.  If <ignore> is given it is
	      also  possible  to  give	an explicit name which will be used when creating arrays.
	      This is the only case when there can be more that one other word	on  the  HOMEHOST

	      When  arrays  are  created,  this  host  name will be stored in the metadata.  When
	      arrays are assembled using auto-assembly, arrays which do not  record  the  correct
	      homehost	name in their metadata will be assembled using a "foreign" name.  A "for-
	      eign" name alway ends with a digit string preceded by an underscore to  differenti-
	      ate it from any possible local name. e.g.  /dev/md/1_1 or /dev/md/home_0.

       AUTO   A  list  of names of metadata format can be given, each preceded by a plus or minus
	      sign.  Also the word homehost is allowed as is all preceded by plus or minus  sign.
	      all is usually last.

	      When  mdadm is auto-assembling an array, either via --assemble or --incremental and
	      it finds metadata of a given type, it  checks  that  metadata  type  against  those
	      listed in this line.  The first match wins, where all matches anything.  If a match
	      is found that was preceded by a plus sign, the auto assembly is  allowed.   If  the
	      match  was  preceded by a minus sign, the auto assembly is disallowed.  If no match
	      is found, the auto assembly is allowed.

	      If the metadata indicates that the array was created for this host,  and	the  word
	      homehost	appears before any other match, then the array is treated as a valid can-
	      didate for auto-assembly.

	      This can be used to disable all  auto-assembly  (so  that  only  arrays  explicitly
	      listed  in mdadm.conf or on the command line are assembled), or to disable assembly
	      of certain metadata types which might be handled by other software.  It can also be
	      used to disable assembly of all foreign arrays - normally such arrays are assembled
	      but given a non-deterministic name in /dev/md/.

	      The known metadata types are 0.90, 1.x, ddf, imsm.

       DEVICE /dev/sd[bcdjkl]1
       DEVICE /dev/hda1 /dev/hdb1

       # /dev/md0 is known by its UUID.
       ARRAY /dev/md0 UUID=3aaa0122:29827cfa:5331ad66:ca767371
       # /dev/md1 contains all devices with a minor number of
       #   1 in the superblock.
       ARRAY /dev/md1 superminor=1
       # /dev/md2 is made from precisely these two devices
       ARRAY /dev/md2 devices=/dev/hda1,/dev/hdb1

       # /dev/md4 and /dev/md5 are a spare-group and spares
       #  can be moved between them
       ARRAY /dev/md4 uuid=b23f3c6d:aec43a9f:fd65db85:369432df
       ARRAY /dev/md5 uuid=19464854:03f71b1b:e0df2edd:246cc977
       # /dev/md/home is created if need to be a partitionable md array
       # any spare device number is allocated.
       ARRAY /dev/md/home UUID=9187a482:5dde19d9:eea3cc4a:d646ab8b

       MAILADDR root@mydomain.tld
       PROGRAM /usr/sbin/handle-mdadm-events
       CREATE group=system mode=0640 auto=part-8
       HOMEHOST <system>
       AUTO +1.x homehost -all

       mdadm(8), md(4).


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