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       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 Linux.

       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 continuation of the previous line.

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

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

              If  no  DEVICE  line  is  present,  then  "DEVICE partitions" is

              For example:

              DEVICE /dev/hda* /dev/hdc*
              DEV    /dev/sd*
              DEVICE /dev/discs/disc*/disc
              DEVICE partitions

       ARRAY  The ARRAY lines identify actual arrays.  The second word on  the
              line  should  be  the  name  of  the  device  where the array is
              normally assembled, such as /dev/md1.  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  interspersed  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.   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  declares to mdadm that it should try to create
                  the device file of the array if it doesn’t already exist, or
                  exists but with the wrong device number.

                  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 indicate 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

              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

              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 — possibly 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 be exactly one other word on the
              line.  It should either exactly <system> or  a  host  name.   If
              <system> is given, then the gethostname(2) systemcall is used to
              get the host name.  When arrays are created, this host name will
              be  stored  in  the  metadata.   When arrays are assembled using
              auto-assembly, only arrays with this host  name  stored  in  the
              metadata will be considered.


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

       # /dev/md0 is known by its UID.
       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>


       mdadm(8), md(4).