.\" -*- nroff -*-
-.TH MDADM 8
+.TH MDADM 8 "" v1.6.0
.SH NAME
mdadm \- manage MD devices
.I aka
(striping),
.B RAID1
(mirroring),
-.B RAID4
+.BR RAID4 ,
+.BR RAID5 ,
+.BR RAID6 ,
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
with a different format and an different purpose.
.SH MODES
-mdadm has 6 major modes of operation:
+mdadm has 7 major modes of operation:
.TP
.B Assemble
Assemble the parts of a previously created
.TP
.B "Follow or Monitor"
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.
+only meaningful for raid1, 4, 5, 6 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 "Grow"
+Grow (or shrink) an array, or otherwise reshape it in some way.
+Currently supported growth options including changing the active size
+of componenet devices in RAID level 1/4/5/6 and changing the number of
+active devices in RAID1.
.SH OPTIONS
.B Monitor
mode.
+.TP
+.BR -G ", " --grow
+Change the size or shape of an active array.
+
.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 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, multipath, mp. Obviously some of these are synonymous.
-Only the first 4 are valid when Building.
+Set raid level. When used with
+.IR --create ,
+options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
+raid5, 5, raid6, 6, multipath, mp. Obviously some of these are synonymous.
+
+When used with
+.IR --build ,
+only linear, raid0, 0, stripe are valid.
.TP
.BR -p ", " --parity=
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
-.B missing
-devices) that are listed on the command line.
+(including "\fBmissing\fP" devices)
+that are listed on the command line for
+.BR --create .
+Setting a value of 1 is probably
+a mistake and so requires that
+.B --force
+be specified first. A value of 1 will then be allowed for linear,
+multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
+.br
+This number can only be changed using
+.B --grow
+for RAID1 arrays, and only on kernels which provide necessary support.
.TP
.BR -x ", " --spare-devices=
.TP
.BR -z ", " --size=
-Amount (in Kibibytes) of space to use from each drive in RAID1/4/5.
+Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
This must be a multiple of the chunk size, and must leave about 128Kb
of space at the end of the drive for the RAID superblock.
If this is not specified
size, though if there is a variance among the drives of greater than 1%, a warning is
issued.
+This value can be set with
+.B --grow
+for RAID level 1/4/5/6. If the array was created with a size smaller
+than the currently active drives, the extra space can be accessed
+using
+.BR --grow .
+
+.TP
+.BR --assume-clean
+Tell
+.I mdadm
+that the array pre-existed and is known to be clean. This is only
+really useful for Building RAID1 array. Only use this if you really
+know what you are doing. This is currently only supported for --build.
+
+.TP
+.BR -R ", " --run
+Insist that
+.I mdadm
+run the array, even if some of the components
+appear to be active in another array or filesystem. Normally
+.I mdadm
+will ask for confirmation before including such components in an
+array. This option causes that question to be suppressed.
+
+.TP
+.BR -f ", " --force
+Insist that
+.I mdadm
+accept the geometry and layout specified without question. Normally
+.I mdadm
+will not allow creation of an array with only one device, and will try
+to create a raid5 array with one missing drive (as this makes the
+initial resync work faster). With
+.BR --force ,
+.I mdadm
+will not try to be so clever.
+
+.TP
+.BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
+Instruct mdadm to create the device file if needed, and to allocate
+an unused minor number. "yes" or "md" causes a non-partitionable array
+to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
+later) to be used. The argumentment can also come immediately after
+"-a". e.g. "-ap".
+
+For partitionable arrays,
+.I mdadm
+will create the device file for the whole array and for the first 4
+partitions. A different number of partitions can be specified at the
+end of this option (e.g.
+.BR --auto=p7 ).
+If the device name ends with a digit, the partition names add an
+underscore, a 'p', and a number, e.g. "/dev/home1_p3". If there is no
+trailing digit, then the partition names just have a number added,
+e.g. "/dev/scratch3".
+
.SH For assemble:
.TP
/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 -a ", " "--auto{=no,yes,md,mdp,part}"
+See this option under Create and Build options.
+
.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
+argument given to this flag can be one of
+.BR sparc2.2 ,
+.BR summaries ,
or
.BR 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
+assembled. This is not needed on 2.6 and later kernels as they make
this adjustment automatically.
+The
+.B summaries
+option will correct the summaries in the superblock. That is the
+counts of total, working, active, failed, and spare devices.
.SH For Manage mode:
the block where the superblock would be is over-written even if it
doesn't appear to be valid.
+.TP
+.BR -t ", " --test
+When used with
+.BR --detail ,
+the exit status of
+.I mdadm
+is set to reflect the status of the device.
+
.SH For Monitor mode:
.TP
.BR -m ", " --mail
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.
+
+.TP
+.BR -1 ", " --oneshot
+Check arrays only once. This will generate
+.B NewArray
+events and more significantly
+.B DegradedArray
+events. Running
+.in +5
+.B " mdadm --monitor --scan -1"
+.in -5
+from a cron script will ensure regular notification of any degraded arrays.
+
+.TP
+.BR -t ", " --test
+Generate a
+.B TestMessage
+alert for every array found at startup. This alert gets mailed and
+passed to the alert program. This can be used for testing that alert
+message to get through successfully.
+
.SH ASSEMBLE MODE
.HP 12
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, then
+.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
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 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
+may work for RAID1, 4, 5 or 6), give the
.B --run
flag.
+If an
+.B auto
+option is given, either on the command line (--auto) or in the
+configuration file (e.g. auto=part), then
+.I mdadm
+will create the md device if necessary or will re-create it if it
+doesn't look usable as it is.
+
+This can be useful for handling partitioned devices (which don't have
+a stable device number - it can change after a reboot) and when using
+"udev" to manage your
+.B /dev
+tree (udev cannot handle md devices because of the unusual device
+initialisation conventions).
+
+If the option to "auto" is "mdp" or "part" or (on the command line
+only) "p", then mdadm will create a partitionable array, using the
+first free one that is not inuse, and does not already have an entry
+in /dev (apart from numeric /dev/md* entries).
+
+If the option to "auto" is "yes" or "md" or (on the command line)
+nothing, then mdadm will create a traditional, non-partitionable md
+array.
+
+It is expected that the "auto" functionality will be used to create
+device entries with meaningful names such as "/dev/md/home" or
+"/dev/md/root", rather than names based on the numerical array number.
+
+When using this option to create a partitionable array, the device
+files for the first 4 partitions are also created. If a different
+number is required it can be simply appended to the auto option.
+e.g. "auto=part8". Partition names are created by appending a digit
+string to the device name, with an intervening "_p" if the device name
+ends with a digit.
+
+The
+.B --auto
+option is also available in Build and Create modes. As those modes do
+not use a config file, the "auto=" config option does not apply to
+these modes.
.SH BUILD MODE
This usage will initialise a new md array, associate some devices with
it, and activate the array.
+This the
+.B --auto
+option is given (as described in more detail in the section on
+Assemble mode), then the md device will be created with a suitable
+device number if necessary.
+
As devices are added, they are checked to see if they contain raid
superblocks or filesystems. They are also checked to see if the variance in
device size exceeds 1%.
can override this caution.
To create a "degraded" array in which some devices are missing, simply
-give the word
-.B missing
+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
-.BR missing .
+"\fBmissing\fP"; for a RAID6 array at most two slots.
For a RAID1 array, only one real device needs to be given. All of the
others can be
-.BR missing .
+"\fBmissing\fP".
+
+When creating a RAID5 array,
+.B mdadm
+will automatically create a degraded array with an extra spare drive.
+This is because building the spare into a degraded array is in general faster than resyncing
+the parity on a non-degraded, but not clean, array. This feature can
+be over-ridden with the
+-I --force
+option.
'''If the
'''.B --size
The General Management options that are valid with --create are:
.TP
.B --run
-insist of running the array even if some devices look like they might
+insist on running the array even if some devices look like they might
be in use.
.TP
will cause the output to be less detailed and the format to be
suitable for inclusion in
.BR /etc/mdadm.conf .
+The exit status of
+.I mdadm
+will normally be 0 unless
+.I mdadm
+failed to get useful information about the device(s). However if the
+.B --test
+option is given, then the exit status will be:
+.RS
+.TP
+0
+The array is functioning normally.
+.TP
+1
+The array has at least one failed device.
+.TP
+2
+The array has multiple failed devices and hence is unusable (raid4 or
+raid5).
+.TP
+4
+There was an error while trying to get information about the device.
+.RE
.TP
--examine
.TP
--stop
-This devices should active md arrays which will be deactivated, if
-they are not currently in use.
+The devices should be active md arrays which will be deactivated, as
+long as they are not currently in use.
.TP
--run
is 20, 40, 60, or 80, this indicates that rebuild has passed that many
percentage of the total.
+.TP
+.B RebuildFinished
+An md array that was rebuilding, isn't any more, either because it
+finished normally or was aborted.
+
.TP
.B Fail
An active component device of an array has been marked as faulty.
.B /proc/mdstat
file.
+.TP
+.B DegradedArray
+A newly noticed array appears to be degraded. This message is not
+generated when
+.I mdadm
+notices a drive failure which causes degradation, but only when
+.I mdadm
+notices that an array is degraded when it first sees the array.
+
.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.
+.TP
+.B TestMessage
+An array was found at startup, and the
+.B --test
+flag was given.
.RE
Only
-.B Fail
+.B Fail ,
+.B FailSpare ,
+.B DegradedArray ,
and
-.B FailSpare
+.B TestMessage
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.
If the removal succeeds but the adding fails, then it is added back to
the original array.
+.SH GROW MODE
+The GROW mode is used for changing the size or shape of an active
+array.
+For this to work, the kernel must support the necessary change.
+Various types of growth may be added during 2.6 development, possibly
+including restructuring a raid5 array to have more active devices.
+
+Currently the only support available is to change the "size" attribute
+for arrays with redundancy, and the raid-disks attribute of RAID1
+arrays.
+
+Normally when an array is build the "size" it taken from the smallest
+of the drives. If all the small drives in an arrays are, one at a
+time, removed and replaced with larger drives, then you could have an
+array of large drives with only a small amount used. In this
+situation, changing the "size" with "GROW" mode will allow the extra
+space to start being used. If the size is increased in this way, a
+"resync" process will start to make sure the new parts of the array
+are synchronised.
+
+Note that when an array changes size, any filesystem that may be
+stored in the array will not automatically grow to use the space. The
+filesystem will need to be explicitly told to use the extra space.
+
+A RAID1 array can work with any number of devices from 1 upwards
+(though 1 is not very useful). There may be times which you want to
+increase or decrease the number of active devices. Note that this is
+different to hot-add or hot-remove which changes the number of
+inactive devices.
+
+When reducing the number of devices in a RAID1 array, the slots which
+are to be removed from the array must already be vacant. That is, the
+devices that which were in those slots must be failed and removed.
+
+When the number of devices is increased, any hot spares that are
+present may be activated immediately.
+
.SH EXAMPLES
.B " mdadm --query /dev/name-of-device"
.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.
projects / thirdparty / mdadm.git / blobdiff