real block devices. This allows multiple devices (typically disk
drives or partitions there-of) to be combined into a single device to
hold (for example) a single filesystem.
-Some RAID levels included redundancy and so can survive some degree of
+Some RAID levels include redundancy and so can survive some degree of
device failure.
-Linux Software RAID devices are implemented through the md (Multiple Devices) device driver.
+Linux Software RAID devices are implemented through the md (Multiple
+Devices) device driver.
Currently, Linux supports
.B LINEAR
.IP \(bu 4
.B mdadm
can perform (almost) all of its functions without having a
-configuration file. Also mdadm helps with management of the configuration
+configuration file. Also
+.B mdadm
+helps with management of the configuration
file.
.IP \(bu 4
.B mdadm
.TP
.BR -A ", " --assemble
-Assemble an existing array.
+Assemble a pre-existing array.
.TP
.BR -B ", " --build
.TP
.BR -p ", " --parity=
Set raid5 parity algorithm. Options are:
-{left,right}-{,a}symmetric, la, ra, ls, rs. The default is left-symmetric.
+left-asymmetric,
+left-symmetric,
+right-asymmetric,
+right-symmetric,
+la, ra, ls, rs. The default is left-symmetric.
.TP
.BR --layout=
.BR -m ", " --super-minor=
Minor number of device that array was created for. Devices which
don't have this minor number are excluded. If you create an array as
-/dev/md1, then all superblock will contain the minor number 1, even if
+/dev/md1, then all superblocks will contain the minor number 1, even if
the array is later assembled as /dev/md2.
.TP
.TP
.BR -r ", " --remove
-remove listed devices. The must not be active. i.e. they should
+remove listed devices. They must not be active. i.e. they should
be failed or spare devices.
.TP
is not given, then the config file will only be used to find the
identity of md arrays.
-Normally the array will be started after it is assembled. However is
+Normally the array will be started after it is assembled. However if
.B --scan
-is not given and insufficient drives were lists to start a complete
+is not given and insufficient drives were listed to start a complete
(non-degraded) array, then the array is not started (to guard against
usage errors). To insist that the array be started in this case (as
may work for RAID1 or RAID5), give the
it, and activate the array.
As devices are added, they are checked to see if they contain raid
-superblocks or filesystems. They are also check to see if the variance in
+superblocks or filesystems. They are also checked to see if the variance in
device size exceeds 1%.
If any discrepancy is found, the array will not automatically be run, though
.B --run
can override this caution.
+To create a "degraded" array in which some devices are missing, simply
+give the word
+.B missing
+in place of a device name. This will cause
+.B mdadm
+to leave the corresponding slot in the array empty.
+For a RAID4 or RAID5 array at most one slot can be
+.BR missing .
+For a RAID1 array, only one real device needs to be given. All of the
+others can be
+.BR missing .
+
'''If the
'''.B --size
'''option is given, it is not necessary to list any component-devices in this command.
removed or added. It is possible to perform multiple operations with
on command. For example:
.br
-mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 /a /dev/hda1
+.B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 /a /dev/hda1"
.br
will firstly mark
.B /dev/hda1
as faulty in
.B /dev/md0
and will then remove it from the array and finally add it back
-in as a spare. However only one md array can be affect by a single
+in as a spare. However only one md array can be affected by a single
command.
.SH MISC MODE
.TP
--detail
-The device should be an active md device. mdadm will display
-a detailed description of the array.
+The device should be an active md device.
+.B mdadm
+will display a detailed description of the array.
.B --brief
-will cause the output to be less detailed and format to be
+or
+.B --scan
+will cause the output to be less detailed and the format to be
suitable for inclusion in
.BR /etc/mdadm.conf .
.TP
--examine
-The device should be a component of an md array. mdadm will
-read the md superblock of the device and display the contents.
+The device should be a component of an md array.
+.B mdadm
+will read the md superblock of the device and display the contents.
If
.B --brief
is given, or
for inclusion in
.BR /etc/mdadm.conf .
-Have
+Having
.B --scan
without listing any devices will cause all devices listed in the
config file to be examined.
.B readonly
array back to being read/write.
+.TP
+--scan
+For all operations except
+.BR --examine ,
+.B --scan
+will cause the operation to be applied to all arrays listed in
+.BR /proc/mdstat .
+For
+.BR --examine,
+.B --scan
+causes all devices listed in the config file to be examined.
+
+
.SH MONITOR MODE
.HP 12
will never exit once it decides that there are arrays to be checked,
so it should normally be run in the background.
+As well as reporting events,
+.B mdadm
+may move a spare drive from one array to another if they are in the
+same
+.B spare-group
+and if the destination array has a failed drive but not spares.
+
If any devices are listed on the command line,
.B mdadm
will only monitor those devices. Otherwise all arrays listed in the
The result of monitoring the arrays is the generation of events.
These events are passed to a separate program (is specified) and may
-be mail to a given E-mail address.
+be mailed to a given E-mail address.
If
Without
.B --scan
.B mdadm
-will continue monitoring along as something was found to monitor. If
+will continue monitoring as long as something was found to monitor. If
no program or email is given, then each event is reported to
.BR stdout .
.RS 4
.TP
.B DeviceDisappeared
-An md array which previously was configured appear to no longer be
+An md array which previously was configured appears to no longer be
configured.
.TP
in the configuration file. The
.B spare-group
name can be any string. It is only necessary that different spare
-groups use different name.
+groups use different names.
When
.B mdadm
If the removal succeeds but the adding fails, then it is added back to
the original array.
+.SH EXAMPLES
+
+To find out if a devices is a raid array or part of one:
+.br
+.B " mdadm -Q /dev/name-of-device"
+
+To assemble and start all array listed in the standard config file:
+.br
+.B " mdadm -As"
+
+To shut down all arrays (that are not still in used):
+.br
+.B " mdadm --stop --scan"
+
+To monitor all arrays if (and only if) an email address or program
+was given in the config file, but poll every 2 minutes:
+.br
+.B " mdadm -Fs --delay=120"
+
+To create /dev/md0 as a RAID1 array with /dev/hda1 and /dev/hdc1:
+.br
+.B " mdadm -C /dev/md0 -l1 -n2 /dev/hd[ac]1"
+
+To create prototype a config file that describes currently
+active arrays that are known to be made from partitions of
+IDE or SCSI drives:
+.br
+.B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
+.br
+.B " mdadm --detail --scan >> mdadm.conf"
+.br
+This file should be reviewed before being used as it may
+contain unwanted detail.
+
+To find out what raid arrays could be assembled from existing
+IDE and SCSI whole drives (not partitions):
+.br
+.B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
+.br
+.B " mdadm -Es -c mdadm.conf >> mdadm.conf"
+This file is very likely to contain unwanted detail, particularly
+the
+.B devices=
+entries.
+
+To get help about Create mode:
+.br
+.B " mdadm --create --help"
+
+To get help about the format of the config file:
+.br
+.B " mdadm --config --help"
+
+To get general help:
+.br
+.B " mdadm --help"
+
+
-'''.SH BUGS
-'''no known bugs.
.SH FILES
.B /proc
filesystem,
.B /proc/mdstat
-gives you informations about md devices status.
-This file is not currently used by
-.BR mdadm .
+lists all active md devices with information about them.
+.B mdadm
+uses this to find arrays when
+.B --scan
+is given in Misc mode, and to monitor array reconstruction
+on Monitor mode.
+
.SS /etc/mdadm.conf
for more details.
-.SH TODO
-
-Finish and document Follow mode.
-
+.SH NOTE
+.B mdadm
+was previously known as
+.BR mdctl .
+
.SH SEE ALSO
For information on the various levels of
RAID, check out:
projects / thirdparty / mdadm.git / blobdiff