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NAME | SYNOPSIS | DESCRIPTION | FILES | EXAMPLE | SEE ALSO | COLOPHON |
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MDADM.CONF(5) File Formats Manual MDADM.CONF(5)
mdadm.conf - configuration for management of Software RAID with
mdadm
/etc/mdadm.conf
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 in any config file, 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.
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.
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.
There should only be one MAILADDR line and it should have
only one address. Any subsequent addresses are silently
ignored.
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
given only one program. Any subsequent programs are
silently ignored.
CREATE The create line gives default values to be used when
creating arrays, new members of arrays, and device entries
for arrays.
There should only be one create line. Any subsequent lines
will override the previous settings.
Keywords used in the CREATE line and supported values are:
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.
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.
names=yes
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.
HOMECLUSTER
The homcluster line gives a default value for the
--homecluster= option to mdadm. It specifies the cluster
name for the md device. The md device can be assembled
only on the cluster which matches the name specified. If
homcluster is not provided, mdadm tries to detect the
cluster name automatically.
There should only be one homecluster line. Any subsequent
lines will be silently ignored.
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 a later config file in a config
directory will not overwrite the setting in an earlier
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=<path_to_file> e.g.
/etc/udev/rules.d/65-md-bare.rules command after changing
the config file. And also run udevadm control --reload
otherwise, a reboot is needed.
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. Lines are applied in reverse order.
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.
MONITORDELAY
The monitordelay line gives a delay in seconds mdadm shall
wait before pooling md arrays when mdadm is running in
--monitor mode. -d/--delay command line argument takes
precedence over the config file.
If multiple MINITORDELAY lines are provided, only first
non-zero value is considered.
ENCRYPTION_NO_VERIFY
The ENCRYPTION_NO_VERIFY disables encryption verification
for devices with particular encryption support detected.
Currently, only verification of SATA OPAL encryption can be
disabled. It does not disable ATA security encryption
verification. Currently effective only for IMSM metadata.
Available parameter sata_opal .
/etc/mdadm.conf
The default config file location, used when mdadm is running
without --config option.
/etc/mdadm.conf.d
The default directory with config files. Used when mdadm is
running without --config option, after successful reading of the
/etc/mdadm.conf default config file. Files in that directory are
read in lexical order.
/etc/mdadm/mdadm.conf
Alternative config file that is read, when mdadm is running
without --config option and the /etc/mdadm.conf default config
file was not opened successfully.
/etc/mdadm/mdadm.conf.d
The alternative directory with config files. Used when mdadm is
runninng without --config option, after reading the
/etc/mdadm/mdadm.conf alternative config file whether it was
successful or not. Files in that directory are read in lexical
order.
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
# 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.
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
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
MONITORDELAY 60
ENCRYPTION_NO_VERIFY sata_opal
mdadm(8), md(4).
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
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-19.) 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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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