mdadm.conf(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | EXAMPLE | SEE ALSO | COLOPHON

MDADM.CONF(5)              File Formats Manual             MDADM.CONF(5)

NAME         top

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

SYNOPSIS         top

       /etc/mdadm.conf

DESCRIPTION         top

       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 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 either or both of
              the  words containers and partitions.  The word containers
              will cause mdadm to look for assembled CONTAINER 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/partitions 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 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 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 indicate 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 container 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, new members of 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 — possibly 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
                  alternative 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.

           bbl=no By default, mdadm will reserve space for a bad block
                  list (bbl) on all devices included in or added to any
                  array that supports them.  Setting bbl=no will prevent
                  this, so newly added devices will not have a bad block
                  log.

       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 <system>, <none>
              and <ignore>.  If <system> is given, then the
              gethostname(2) systemcall is used to get the host name.
              This is the default.

              If <ignore> is given, then a flag is set so that when
              arrays are being auto-assembled 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 line.  If
              there are other words, or other HOMEHOST lines, they are
              silently ignored.

              If <none> 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 "foreign" name alway ends with a digit string
              preceded by an underscore to differentiate 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 candidate 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 appearing 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 contains 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 command after changing the
              config file

              Keywords 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 irrelevant 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

       PART-POLICY
              This is similar to POLICY and accepts the same keyword
              assignments.  It allows a consistent set of policies to
              applied to each of the partitions of a device.

              A PART-POLICY line should set type=disk and identify the
              path to one or more disk devices.  Each partition on these
              disks will be treated according to the action= setting
              from this line.  If a domain is set in the line, then the
              domain associated with each patition will be based on the
              domain, but with "-partN" appended, when N is the
              partition number for the partition that was found.

       SYSFS  The SYSFS line lists custom values of MD device's sysfs
              attributes which will be stored in sysfs after the array
              is assembled. Multiple lines are allowed and each line has
              to contain the uuid or the name of the device to which it
              relates.

           uuid=  hexadecimal identifier of MD device. This has to match
                  the uuid stored in the superblock.

           name=  name of the MD device as was given to mdadm when the
                  array was created. It will be ignored if uuid is not
                  empty.

EXAMPLE         top

              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 <system>
              AUTO +1.x homehost -all
              SYSFS name=/dev/md/raid5 group_thread_cnt=4
              sync_speed_max=1000000
              SYSFS uuid=bead5eb6:31c17a27:da120ba2:7dfda40d
              group_thread_cnt=4 sync_speed_max=1000000

SEE ALSO         top

       mdadm(8), md(4).

COLOPHON         top

       This page is part of the mdadm (Tool for managing md arrays in
       Linux) project.  Information about the project can be found at 
       ⟨http://neil.brown.name/blog/mdadm⟩.  If you have a bug report for
       this manual page, send it to linux-raid@vger.kernl.org.  This
       page was obtained from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/⟩ on
       2021-04-01.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

                                                           MDADM.CONF(5)

Pages that refer to this page: mdadm(8)raid6check(8)