mdadm.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
Some common tasks, such as assembling all arrays, can be simplified by describing the
devices and arrays in this configuration file.
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 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-
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.
DEVICE /dev/hda* /dev/hdc*
ARRAY 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 /dev/md1. Subse-
quent 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.
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. Precisely these devices
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.
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.
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.
The mailaddr line gives an E-mail address that alerts should be sent to when 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.
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.
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/hda2
# /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