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 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 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.

For example:

DEVICE /dev/hda* /dev/hdc*

DEV /dev/sd*

DEVICE /dev/discs/disc*/disc

DEVICE partitions

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. 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.

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 declares to mdadm 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.

MAILADDR

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.

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.