.\" -*- nroff -*-
-.TH mdadm 8
+.TH MDADM 8 "" v1.2.0
.SH NAME
mdadm \- manage MD devices
.I aka
.SH SYNOPSIS
-.BI mdadm " [mode] <raiddevice> [options] <subdevices>"
+.BI mdadm " [mode] <raiddevice> [options] <component-devices>"
.SH DESCRIPTION
RAID devices are virtual devices created from two or more
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
-does not support 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
-can provide information about your arrays (through Detail and Examine)
+can provide information about your arrays (through Query, Detail, and Examine)
that
.B raidtools
cannot.
-.IP \(bu 4
+.P
+.I mdadm
+does not use
+.IR /etc/raidtab ,
+the
.B raidtools
-can manage MULTIPATH devices which
-.B mdadm
-cannot yet manage.
+configuration file, at all. It has a different configuration file
+with a different format and an different purpose.
.SH MODES
-mdadm has 7 major modes of operation:
+mdadm has 6 major modes of operation:
.TP
.B Assemble
Assemble the parts of a previously created
'''in several step create-add-add-run or it can all happen with one command.
.TP
-.B Detail
-Display the details of a given md device. Details include the RAID
-level, the number of devices, which ones are faulty (if any), and the
-array UUID.
+.B Manage
+This is for doing things to specific components of an array such as
+adding new spares and removing faulty devices.
.TP
-.B Examine
-Examine a device to see if it is part of an md array, and print out
-the details of that array.
-This mode can also be used to examine a large number of devices and to
-print out a summary of the arrays found in a format suitable for the
-.B mdadm.conf
-configuration file.
+.B Misc
+This mode allows operations on independent devices such as examine MD
+superblocks, erasing old superblocks and stopping active arrays.
.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.
-.TP
-.B Manage
-This is for odd bits an pieces like hotadd, hotremove, setfaulty, stop,
-readonly, readwrite.
-'''If an array is only partially setup by the
-'''Create or Assemble commands, subsequent Manage commands can finish the
-'''job.
.SH OPTIONS
.TP
.BR -A ", " --assemble
-Assemble an existing array.
+Assemble a pre-existing array.
.TP
.BR -B ", " --build
.BR -C ", " --create
Create a new array.
+.TP
+.BR -Q ", " --query
+Examine a device to see
+(1) if it is an md device and (2) if it is a component of an md
+array.
+Information about what is discovered is presented.
+
.TP
.BR -D ", " --detail
Print detail of one or more md devices.
.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
and
.BR --examine .
+.TP
+.BR -f ", " --force
+Be more forceful about certain operations. See the various modes of
+the exact meaning of this option in different contexts.
+
+.TP
+.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
+scan config file or
+.B /proc/mdstat
+for missing information.
+In general, this option gives
+.B mdadm
+permission to get any missing information, like component devices,
+array devices, array identities, and alert destination from the
+configuration file:
+.BR /etc/mdadm.conf .
+One exception is MISC mode when using
+.B --detail
+or
+.B --stop
+in which case
+.B --scan
+says to get a list of array devices from
+.BR /proc/mdstat .
+
.SH For create or build:
.TP
.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.
-.TP
-.BR -c ", " --config=
-config file. Default is
-.BR /etc/mdadm.conf .
-
-.TP
-.BR -s ", " --scan
-scan config file for missing information
+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
.B --run
an attempt will be made to start it anyway.
-.SH General management
+.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
.BR -a ", " --add
.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
.BR -R ", " --run
start a partially built array.
.BR -w ", " --readwrite
mark array as readwrite.
+.TP
+.B --zero-superblock
+If the device contains a valid md superblock, the block is
+over-written with zeros. With
+--force
+the block where the superblock would be is over-written even if it
+doesn't appear to be valid.
+
+.SH For Monitor mode:
+.TP
+.BR -m ", " --mail
+Give a mail address to send alerts to.
+
+.TP
+.BR -p ", " --program ", " --alert
+Give a program to be run whenever an event is detected.
+
+.TP
+.BR -d ", " --delay
+Give a delay in seconds.
+.B mdadm
+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 ASSEMBLY MODE
+.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
.PP
This usage assembles one or more raid arrays from pre-existing components.
For each array, mdadm needs to know the md device, the identity of the
-array, and a number of sub devices. These can be found in a number of ways.
+array, and a number of component-devices. These can be found in a number of ways.
+
+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.
-The md device is either given before
+If precisely one device is listed, but
.B --scan
-or is found from the config file. In the latter case, multiple md devices
-can be started with a single mdadm command.
+is not given, that
+.I mdadm
+acts as though
+.B --scan
+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
-super block on the first subdevice listed on the command line.
+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 subdevices in this command.
+'''option is given, it is not necessary to list any component-devices in this command.
'''They can be added later, before a
'''.B --run.
'''If no
.B --readonly
start the array readonly - not supported yet.
-.SH DETAIL MODE
+.SH MANAGE MODE
.HP 12
Usage:
-.B mdadm --detail
-.RB [ --brief ]
-.I device ...
+.B mdadm
+.I device
+.I options... devices...
.PP
-This usage sill print out the details of the given array including a
-list of component devices. To determine names for the devices,
+This usage will allow individual devices in an array to be failed,
+removed or added. It is possible to perform multiple operations with
+on command. For example:
+.br
+.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 affected by a single
+command.
+
+.SH MISC MODE
+.HP 12
+Usage:
.B mdadm
-searches
-.B /dev
-for device files with the right major and minor numbers.
+.I options ...
+.I devices ...
+.PP
-With
+MISC mode includes a number if distinct operations that
+operate on distinct devices. The operations are:
+.TP
+--query
+The device is examined to see if it is
+(1) an active md array, or
+(2) a component of an md array.
+The information discovered is reported.
+
+.TP
+--detail
+The device should be an active md device.
+.B mdadm
+will display a detailed description of the array.
.B --brief
+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.
.B mdadm
-prints a single line that identifies the level, number of disks, and
-UUID of the array. This line is suitable for inclusion in
+will read the md superblock of the device and display the contents.
+If
+.B --brief
+is given, or
+.B --scan
+then multiple devices that are components of the one array
+are grouped together and reported in a single entry suitable
+for inclusion in
.BR /etc/mdadm.conf .
-.SH EXAMINE MODE
+Having
+.B --scan
+without listing any devices will cause all devices listed in the
+config file to be examined.
+
+.TP
+--stop
+This devices should active md arrays which will be deactivated, if
+they are not currently in use.
+
+.TP
+--run
+This will fully activate a partially assembled md array.
+
+.TP
+--readonly
+This will mark an active array as read-only, providing that it is
+not currently being used.
+
+.TP
+--readwrite
+This will change a
+.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
Usage:
-.B mdadm --examine
-.RB [ --scan ]
-.RB [ --brief ]
-.I device ...
+.B mdadm --monitor
+.I options... devices...
+
.PP
-This usage will examine some block devices to see if that have a valid
-RAID superblock on them. The information in each valid raid
-superblock will be printed.
+This usage causes
+.B mdadm
+to periodically poll a number of md arrays and to report on any events
+noticed.
+.B mdadm
+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
+configuration file will be monitored. Further, if
+.B --scan
+is given, then any other md devices that appear in
+.B /proc/mdstat
+will also be monitored.
+
+The result of monitoring the arrays is the generation of events.
+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
-is used, the no devices should be listed, and the complete set of
-devices identified in the configuration file are checked.
+is given, then a program or an E-mail address must be specified on the
+command line or in the config file. If neither are available, then
+.B mdadm
+will not monitor anything.
+Without
.B --scan
-implies
-.B --brief
-but this implication can be countered by specifying
-.BR --verbose .
+.B mdadm
+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 .
-With
-.B --brief
+The different events are:
+
+.RS 4
+.TP
+.B DeviceDisappeared
+An md array which previously was configured appears to no longer be
+configured.
+
+.TP
+.B RebuildStarted
+An md array started reconstruction.
+
+.TP
+.BI Rebuild NN
+Where
+.I NN
+is 20, 40, 60, or 80, this indicates that rebuild has passed that many
+percentage of the total.
+
+.TP
+.B Fail
+An active component device of an array has been marked as faulty.
+
+.TP
+.B FailSpare
+A spare component device which was being rebuilt to replace a faulty
+device has failed.
+
+.TP
+.B SpareActive
+A spare component device which was being rebuilt to replace a faulty
+device as been successfully rebuild and has been made active.
+
+.TP
+.B NewArray
+A new md array has been detected in the
+.B /proc/mdstat
+file.
+
+.TP
+.B MoveSpare
+A spare drive has been moved from one array in a
+.B spare-group
+to another to allow a failed drive to be replaced.
+
+.RE
+
+Only
+.B Fail
+and
+.B FailSpare
+cause Email to be sent. All events cause the program to be run.
+The program is run with two or three arguments, they being the event
+name, the array device and possibly a second device.
+
+Each event has an associated array device (e.g.
+.BR /dev/md1 )
+and possibly a second device. For
+.BR Fail ,
+.BR FailSpare ,
+and
+.B SpareActive
+the second device is the relevant component device.
+For
+.B MoveSpare
+the second device is the array that the spare was moved from.
+
+For
.B mdadm
-will output an config file entry of each distinct array that was
-found. This entry will list the UUID, the raid level, and a list of
-the individual devices on which a superblock for that array was found.
-This output will by syntactically suitable for inclusion in the
-configuration file, but should
-.B NOT
-be used blindly. Often the array description that you want in the
-configuration file is much less specific than that given by
-.BR "mdadm -Bs" .
-For example, you normally do not want to list the devices,
-particularly if they are SCSI devices.
-
-'''.SH BUGS
-'''no known bugs.
+to move spares from one array to another, the different arrays need to
+be labelled with the same
+.B spare-group
+in the configuration file. The
+.B spare-group
+name can be any string. It is only necessary that different spare
+groups use different names.
+
+When
+.B mdadm
+detects that an array which is in a spare group has fewer active
+devices than necessary for the complete array, and has no spare
+devices, it will look for another array in the same spare group that
+has a full complement of working drive and a spare. It will then
+attempt to remove the spare from the second drive and add it to the
+first.
+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 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