MDADM.CONFSection: File Formats (5)
Index Return to Main Contents
NAMEmdadm.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.
SYNTAXThe 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:
line lists the devices (whole devices or partitions) that might contain
a component of an MD array. When looking for the components of an
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 there-in. 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" is assumed.
DEVICE /dev/hda* /dev/hdc*
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
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:
- The value should be a 128 bit uuid in hexadecimal, with punctuation interspersed if desired. This must match the uuid stored in the superblock.
- 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.
- 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.
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
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.
will report an array if it is found to have fewer than this number of
starts or when
The value is a textual name for a group of arrays. All arrays with
name are considered to be part of the same group. The significance of
a group of arrays is that
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.
This option declares to
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,
will provide this file to the
driver as the bitmap file. This has the same function as the
Specify the metadata format that the array has. This is mainly
recognised for comparability with the output of
line gives an E-mail address that alerts should be
sent to when
is running in
mode (and was given the
option). There should only be one
line and it should have only one address.
line (which can only be abbreviate at leat 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.
line gives the name of a program to be run when
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
There should only be one program line and it should be give only one program.
line gives default values to be used when creating arrays and device entries for
- These can give user/group ids or names to use instead of system defaults (root/wheel or root/disk).
- An octal file mode such as 0660 can be given to override the default of 0600.
This corresponds to the
flag to mdadm. Give
- 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 symlinked=no to suppress this symlink creation.
DEVICE /dev/hda1 /dev/hdb1
# /dev/md0 is known by it's 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 precisey 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
CREATE group=system mode=0640 auto=part-8
SEE ALSOmdadm(8), md(4).