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MDADM.CONF(5) MDADM.CONF(5)
NAME
mdadm.conf - configuration for management of Software RAID with mdadm
SYNOPSIS
/etc/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 configu-
ration 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.
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 key-
words 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 of both of the words containers and partitions. The word con-
tainers will cause mdadm to look for assembled CONTAINER arrays and included them as a source for assembling fur-
ther 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 out-
put 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 compatibil-
ity 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.
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 -- 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 start-
ing md or md_. Give symlinks=no to suppress this symlink creation.
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> 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-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.
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 "for-
eign" 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 com-
mand line are assembled), or to disable assembly of certain metadata types which might be handled by other soft-
ware. 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.
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
MAILADDR rootATmydomain.tld
PROGRAM /usr/sbin/handle-mdadm-events
CREATE group=system mode=0640 auto=part-8
HOMEHOST <system>
AUTO +1.x homehost -all
SEE ALSO
mdadm(8), md(4).
MDADM.CONF(5)
