mdadm.conf <root
MDADM.CONF(5)                          File Formats Manual                          MDADM.CONF(5)

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

SYNOPSIS
       /etc/mdadm/mdadm.conf

DESCRIPTION
       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.

   SYNTAX
       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.

       Spaces  can be included in a word using quotation characters.  Either single quotes (') or
       double quotes (") may be used.  All the characters from one quotation  character  to  next
       identical  character  are  protected  and  will not be used to separate words to start new
       quoted strings.  To include a single quote it must be between double quotes.  To include a
       double quote it must be between single quotes.

       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‐
       acters.

       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 or 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  (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
                  names.

           super-minor=
                  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.

           devices=
                  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.

           num-devices=
                  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.

           spares=
                  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.

           spare-group=
                  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.

           bitmap=
                  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
                  --assemble.

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

           container=
                  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.

           member=
                  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.

       MAILADDR
              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.  Any subsequent addresses
              are silently ignored.

       MAILFROM
              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.

       PROGRAM
              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:

           owner=

           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 — possi‐
                  bly followed by a number of partitions — to indicate how missing device entries
                  should be created.

           metadata=
                  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.

           symlinks=no
                  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.

           names=yes
                  Since  Linux  2.6.29 it has been possible to create md devices with a name like
                  md_home rather than just a number, like md3.  mdadm will use the numeric alter‐
                  native  by  default as other tools that interact with md arrays may expect only
                  numbers.  If names=yes is given in mdadm.conf then mdadm will use a  name  when
                  appropriate.   If  names=no is given, then non-numeric md device names will not
                  be used even if the default changes in a future release of mdadm.

       HOMEHOST
              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 ,  and .   If    is
              given,  then  the  gethostname(2) systemcall is used to get the host name.  This is
              the default.

              If  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  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
              line.  If there are other  words,  or  other  HOMEHOST  lines,  they  are  silently
              ignored.

              If   is given, then the default of using gethostname(2) is over-ridden and no
              homehost name is assumed.

              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.

              AUTO should be given at most once.  Subsequent lines are silently ignored.  Thus an
              earlier config file in a config directory will over-ride the  setting  in  a  later
              config file.

       POLICY This is used to specify what automatic behavior is allowed on devices newly appear‐
              ing in the system and provides a way of marking spares that can be moved  to  other
              arrays as well as the migration domains.  Domain can be defined through policy line
              by specifying a domain name for a  number  of  paths  from  /dev/disk/by-path/.   A
              device  may belong to several domains. The domain of an array is a union of domains
              of all devices in that array.  A spare can be automatically moved from one array to
              another if the set of the destination array's domains ppcontains all the domains of
              the new disk or if both arrays have the same spare-group.

              To update hot plug configuration it is necessary to execute mdadm --udev-rules com‐
              mand after changing the config file

              Key words used in the POLICY line and supported values are:

              domain=
                     any arbitrary string

              metadata=
                     0.9 1.x ddf or imsm

              path=  file glob matching anything from /dev/disk/by-path

              type=  either disk or part.

              action=
                     include,  re-add,  spare,  spare-same-slot, or force-spare auto= yes, no, or
                     homehost.

              The action item determines the automatic behavior allowed for devices matching  the
              path  and  type in the same line.  If a device matches several lines with different
              actions then the most permissive will apply. The ordering of policy lines is irrel‐
              evant to the end result.

              include
                     allows adding a disk to an array if metadata on that disk matches that array

              re-add will include the device in the array if it appears to be a current member or
                     a member that was recently removed and the array has  a  write-intent-bitmap
                     to allow the re-add functionality.

              spare  as  above  and  additionally: if the device is bare it can become a spare if
                     there is any array that it is a candidate for based on domains and metadata.

              spare-same-slot
                     as above and additionally if given slot was  used  by  an  array  that  went
                     degraded  recently and the device plugged in has no metadata then it will be
                     automatically added to that array (or it's container)

              force-spare
                     as above and the disk will become a spare in remaining cases

EXAMPLE
       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
                  spare-group=group1
       ARRAY /dev/md5 uuid=19464854:03f71b1b:e0df2edd:246cc977
                  spare-group=group1
       # /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
                  auto=part
       # The name of this array contains a space.
       ARRAY /dev/md9 name='Data Storage'

       POLICY domain=domain1 metadata=imsm path=pci-0000:00:1f.2-scsi-*
                  action=spare
       POLICY domain=domain1 metadata=imsm path=pci-0000:04:00.0-scsi-[01]*
                  action=include
       # One domain comprising of devices attached to specified paths is defined.
       # Bare device matching first path will be made an imsm spare on hot plug.
       # If more than one array is created on devices belonging to domain1 and
       # one of them becomes degraded, then any imsm spare matching any path for
       # given domain name can be migrated.
       MAILADDR root@mydomain.tld
       PROGRAM /usr/sbin/handle-mdadm-events
       CREATE group=system mode=0640 auto=part-8
       HOMEHOST 
       AUTO +1.x homehost -all

SEE ALSO
       mdadm(8), md(4).

                                                                                    MDADM.CONF(5)

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