.\" -*- nroff -*-
-.TH MDADM 8
+.TH MDADM 8 "" v1.2.0
.SH NAME
mdadm \- manage MD devices
.I aka
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
(striping),
.B RAID1
(mirroring),
-.B RAID4
+.BR RAID4 ,
+.BR RAID5 ,
and
-.B RAID5.
-
-Recent kernels (2002) also support a mode known as
.BR MULTIPATH .
-.B mdadm
-only provides limited support for MULTIPATH as yet.
+
+.B MULTIPATH is not a Software RAID mechanism, but does involve
+multiple devices. For
+.B MULTIPATH
+each device is a path to one common physical storage device.
+
.B mdadm
is a program that can be used to create, manage, and monitor
.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 and does not use one by default. Also
+.B mdadm
+helps with management of the configuration
file.
.IP \(bu 4
.B mdadm
that
.B raidtools
cannot.
+.P
+.I mdadm
+does not use
+.IR /etc/raidtab ,
+the
+.B raidtools
+configuration file, at all. It has a different configuration file
+with a different format and an different purpose.
.SH MODES
mdadm has 6 major modes of operation:
.TP
.B "Follow or Monitor"
-Monitor one or more md devices and act on any state changes.
+Monitor one or more md devices and act on any state changes. This is
+only meaningful for raid1, raid5 or multipath arrays as only these have
+interesting state. raid0 or linear never have missing, spare, or
+failed drives, so there is nothing to monitor.
+
.SH OPTIONS
.TP
.BR -A ", " --assemble
-Assemble an existing array.
+Assemble a pre-existing array.
.TP
.BR -B ", " --build
.TP
.BR -h ", " --help
-Display help message or, after above option, mode specific help message.
+Display help message or, after above option, mode specific help
+message.
+
+.TP
+.B --help-options
+Display more detailed help about command line parsing and some commonly
+used options.
.TP
.BR -V ", " --version
.BR -c ", " --config=
Specify the config file. Default is
.BR /etc/mdadm.conf .
+If the config file given is
+.B partitions
+then nothing will be read, but
+.I mdadm
+will act as though the config file contained exactly
+.B "DEVICE partitions"
+and will read
+.B /proc/partitions
+to find a list of devices to scan.
+If the word
+.B none
+is given for the config file, then
+.I mdadm
+will act as though the config file were empty.
.TP
.BR -s ", " --scan
.TP
.BR -l ", " --level=
Set raid level. Options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid5, 4,
-raid5, 5. Obviously some of these are synonymous.
+raid5, 5, multipath, mp. Obviously some of these are synonymous.
Only the first 4 are valid when Building.
.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=
same as --parity
.TP
-.BR -n ", " --raid-disks=
-number of active devices in array.
+.BR -n ", " --raid-devices=
+Specify the number of active devices in the array. This, plus the
+number of spare devices (see below) must equal the number of
+.I component-devices
+(including "\fBmissing\fP" devices)
+that are listed on the command line.
.TP
-.BR -x ", " --spare-disks=
-number of spare (eXtra) disks in initial array. Spares can be added
-and removed later.
+.BR -x ", " --spare-devices=
+Specify the number of spare (eXtra) devices in the initial array.
+Spares can also be added
+and removed later. The number of component devices listed
+on the command line must equal the number of raid devices plus the
+number of spare devices.
+
.TP
.BR -z ", " --size=
.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.
+Giving the literal word "dev" for
+.B --super-minor
+will cause
+.I mdadm
+to use the minor number of the md device that is being assembled.
+e.g. when assembling
+.BR /dev/md0 ,
+.M --super-minor=dev
+will look for super blocks with a minor number of 0.
+
.TP
.BR -f ", " --force
Assemble the array even if some superblocks appear out-of-date
.B --run
an attempt will be made to start it anyway.
+.TP
+.BR -U ", " --update=
+Update the superblock on each device while assembling the array. The
+argument given to this flag can be either
+.B sparc2.2
+or
+.BR super-minor .
+
+The
+.B sparc2.2
+option will adjust the superblock of an array what was created on a Sparc
+machine running a patched 2.2 Linux kernel. This kernel got the
+alignment of part of the superblock wrong. You can use the
+.B "--examine --sparc2.2"
+option to
+.I mdadm
+to see what effect this would have.
+
+The
+.B super-minor
+option will update the
+.B "prefered minor"
+field on each superblock to match the minor number of the array being
+assembled. This is not need on 2.6 and later kernels as they make
+this adjustment automatically.
+
+
.SH For Manage mode:
.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
.BR --set-faulty
same as --fail.
+.SH For Examine mode:
+
+.TP
+.B --sparc2.2
+In an array was created on a 2.2 Linux kernel patched with RAID
+support, the superblock will have been created incorrectly, or at
+least incompatibly with 2.4 and later kernels. Using the
+.B --sparc2.2
+flag with
+.B --examine
+will fix the superblock before displaying it. If this appears to do
+the right thing, then the array can be successfully assembled using
+.BR "--assemble --update=sparc2.2" .
+
.SH For Misc mode:
.TP
polls the md arrays and then waits this many seconds before polling
again. The default is 60 seconds.
+.TP
+.BR -f ", " --daemonise
+Tell
+.B mdadm
+to run as a background daemon if it decides to monitor anything. This
+causes it to fork and run in the child, and to disconnect form the
+terminal. The process id of the child is written to stdout.
+This is useful with
+.B --scan
+which will only continue monitoring if a mail address or alert program
+is found in the config file.
+
.SH ASSEMBLE MODE
.HP 12
Usage:
.B mdadm --assemble
-.I device options...
+.I md-device options-and-component-devices...
+.HP 12
+Usage:
+.B mdadm --assemble --scan
+.I md-devices-and-options...
.HP 12
Usage:
.B mdadm --assemble --scan
For each array, mdadm needs to know the md device, the identity of the
array, and a number of component-devices. These can be found in a number of ways.
-The md device is either given before
+In the first usage example (without the
+.BR --scan )
+the first device given is the md device.
+In the second usage example, all devices listed are treated as md
+devices and assembly is attempted.
+In the third (where no devices are listed) all md devices that are
+listed in the configuration file are assembled.
+
+If precisely one device is listed, but
+.B --scan
+is not given, that
+.I mdadm
+acts as though
.B --scan
-or is found from the config file. In the latter case, multiple md devices
-can be started with a single mdadm command.
+was given and identify information is extracted from the configuration file.
The identity can be given with the
.B --uuid
option, with the
.B --super-minor
-option, can be found in in the config file, or will be taken from the
+option, can be found in the config file, or will be taken from the
super block on the first component-device listed on the command line.
Devices can be given on the
.B --assemble
-command line or from the config file. Only devices which have an md
-superblock which contains the right identity will be considered for any device.
+command line or in the config file. Only devices which have an md
+superblock which contains the right identity will be considered for
+any array.
The config file is only used if explicitly named with
.B --config
-or requested with
+or requested with (a possibly implicit)
.B --scan.
In the later case,
.B /etc/mdadm.conf
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
.I device
.BI --chunk= X
.BI --level= Y
-.BI --raid-disks= Z
+.BI --raid-devices= Z
.I devices
.PP
.BI --chunk= X
.BI --level= Y
.br
-.BI --raid-disks= Z
+.BI --raid-devices= Z
.I devices
.PP
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 "\fBmissing\fP"
+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
+"\fBmissing\fP".
+For a RAID1 array, only one real device needs to be given. All of the
+others can be
+"\fBmissing\fP".
+
'''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
will also be monitored.
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.
+These events are passed to a separate program (if specified) and may
+be mailed to a given E-mail address.
+When passing event to program, the program is run once for each event
+and is given 2 or 3 command-line arguements. The first is the
+name of the event (see below). The second is the name of the
+md device which is affected, and the third is the name of a related
+device if relevant, such as a component device that has failed.
If
.B --scan
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
+
+.B " mdadm --query /dev/name-of-device"
+.br
+This will find out if a given device is a raid array, or is part of
+one, and will provide brief information about the device.
+
+.B " mdadm --assemble --scan"
+.br
+This will assemble and start all arrays listed in the standard confile
+file. This command will typically go in a system startup file.
+
+.B " mdadm --stop --scan"
+.br
+This will shut down all array that can be shut down (i.e. are not
+currently in used). This will typically going in a system shutdown script.
+
+.B " mdadm --follow --scan --delay=120"
+.br
+If (and only if) there is an Email address or program given in the
+standard config file, then
+monitor the status of all arrays listed in that file by
+polling them ever 2 minutes.
+
+.B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
+.br
+Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
+
+.br
+.B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
+.br
+.B " mdadm --detail --scan >> mdadm.conf"
+.br
+This will create a prototype config file that describes currently
+active arrays that are known to be made from partitions of IDE or SCSI drives.
+This file should be reviewed before being used as it may
+contain unwanted detail.
+
+.B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
+.br
+.B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
+.ber
+This will find what arrays could be assembled from existign IDE and
+SCSI whole drives (not partitions) and store the information is the
+format of a config file.
+This file is very likely to contain unwanted detail, particularly
+the
+.B devices=
+entries. It should be reviewed and edited before being used as an
+actual config file.
+
+.B " mdadm --examine --brief --scan --config=partitions"
+.br
+.B " mdadm -Ebsc partitions"
+.br
+Create a list of devices by reading
+.BR /proc/partitions ,
+scan these for RAID superblocks, and printout a brief listing of all
+that was found.
+
+.B " mdadm -Ac partitions -m 0 /dev/md0"
+.br
+Scan all partitions and devices listed in
+.BR /proc/partitions
+and assemble
+.B /dev/md0
+out of all such devices with a RAID superblock with a minor number of 0.
+
+.B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
+.br
+If config file contains a mail address or alert program, run mdadm in
+the background in monitor mode monitoring all md devices. Also write
+pid of mdadm daemon to
+.BR /var/run/mdadm .
+
+.B " mdadm --create --help"
+.br
+Providew help about the Create mode.
+
+.B " mdadm --config --help"
+.br
+Provide help about the format of the config file.
+
+.B " mdadm --help"
+.br
+Provide general 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