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:

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:

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 command after changing the config file

Keywords used in the POLICY line and supported values are:

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.

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.

/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.