.\" -*- nroff -*-
-.TH MDADM 8 "" v1.1.0
+''' Copyright Neil Brown and others.
+''' This program is free software; you can redistribute it and/or modify
+''' it under the terms of the GNU General Public License as published by
+''' the Free Software Foundation; either version 2 of the License, or
+''' (at your option) any later version.
+''' See file COPYING in distribution for details.
+.TH MDADM 8 "" v2.5.6
.SH NAME
mdadm \- manage MD devices
.I aka
.BI mdadm " [mode] <raiddevice> [options] <component-devices>"
-.SH DESCRIPTION
+.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
(mirroring),
.BR RAID4 ,
.BR RAID5 ,
+.BR RAID6 ,
+.BR RAID10 ,
+.BR MULTIPATH ,
and
-.BR MULTIPATH .
+.BR FAULTY .
-.B MULTIPATH is not a Software RAID mechanism, but does involve
+.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
-MD devices. As
-such it provides a similar set of functionality to the
-.B raidtools
-packages.
-The key differences between
-.B mdadm
-and
-.B raidtools
-are:
-.IP \(bu 4
-.B mdadm
-is a single program and not a collection of programs.
-.IP \(bu 4
-.B mdadm
-can perform (almost) all of its functions without having a
-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 Query, Detail, and Examine)
-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.
+.B FAULTY
+is also not true RAID, and it only involves one device. It
+provides a layer over a true device that can be used to inject faults.
+
+'''.B mdadm
+'''is a program that can be used to create, manage, and monitor
+'''MD devices. As
+'''such it provides a similar set of functionality to the
+'''.B raidtools
+'''packages.
+'''The key differences between
+'''.B mdadm
+'''and
+'''.B raidtools
+'''are:
+'''.IP \(bu 4
+'''.B mdadm
+'''is a single program and not a collection of programs.
+'''.IP \(bu 4
+'''.B mdadm
+'''can perform (almost) all of its functions without having a
+'''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 Query, Detail, and Examine)
+'''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 a 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
array into an active array. Components can be explicitly given
-or can be searched for.
+or can be searched for.
.B mdadm
checks that the components
do form a bona fide array, and can, on request, fiddle superblock
.TP
.B Build
-Build a legacy array without per-device superblocks.
+Build an array that doesn't have per-device superblocks. For these
+sorts of arrays,
+.I mdadm
+cannot differentiate between initial creation and subsequent assembly
+of an array. It also cannot perform any checks that appropriate
+devices have been requested. Because of this, the
+.B Build
+mode should only be used together with a complete understanding of
+what you are doing.
.TP
.B Create
'''It can progress
'''in several step create-add-add-run or it can all happen with one command.
+.TP
+.B "Follow or Monitor"
+Monitor one or more md devices and act on any state changes. This is
+only meaningful for raid1, 4, 5, 6, 10 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 component devices in RAID level 1/4/5/6 and changing the number of
+active devices in RAID1.
+
.TP
.B Manage
This is for doing things to specific components of an array such as
.TP
.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. 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.
-
+This is an 'everything else' mode that supports operations on active
+arrays, operations on component devices such as erasing old superblocks, and
+information gathering operations.
+'''This mode allows operations on independent devices such as examine MD
+'''superblocks, erasing old superblocks and stopping active arrays.
.SH OPTIONS
-Available options are:
+.SH Options for selecting a mode are:
.TP
.BR -A ", " --assemble
.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 -E ", " --examine
-Print content of md superblock on device(s).
-
.TP
.BR -F ", " --follow ", " --monitor
Select
.B Monitor
mode.
+.TP
+.BR -G ", " --grow
+Change the size or shape of an active array.
+.P
+If a device is given before any options, or if the first option is
+.BR --add ,
+.BR --fail ,
+or
+.BR --remove ,
+then the MANAGE mode is assume.
+Anything other than these will cause the
+.B Misc
+mode to be assumed.
+
+.SH Options that are not mode-specific are:
+
.TP
.BR -h ", " --help
-Display help message or, after above option, mode specific help message.
+Display general help message or, after one of the above options, a
+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
.TP
.BR -v ", " --verbose
-Be more verbose about what is happening.
+Be more verbose about what is happening. This can be used twice to be
+extra-verbose.
+The extra verbosity currently only affects
+.B --detail --scan
+and
+.BR "--examine --scan" .
+
+.TP
+.BR -q ", " --quiet
+Avoid printing purely informative messages. With this,
+.B mdadm
+will be silent unless there is something really important to report.
.TP
.BR -b ", " --brief
.B --detail
and
.BR --examine .
+Using
+.B --brief
+with
+.B --verbose
+gives an intermediate level of verbosity.
.TP
.BR -f ", " --force
.TP
.BR -c ", " --config=
-Specify the config file. Default is
-.BR /etc/mdadm.conf .
+Specify the config file. Default is to use
+.BR /etc/mdadm.conf ,
+or if that is missing, then
+.BR /etc/mdadm/mdadm.conf .
If the config file given is
.B partitions
then nothing will be read, but
says to get a list of array devices from
.BR /proc/mdstat .
-.SH For create or build:
-
.TP
-.BR -c ", " --chunk=
-Specify chunk size of kibibytes. The default is 64.
+.B -e ", " --metadata=
+Declare the style of superblock (raid metadata) to be used. The
+default is 0.90 for --create, and to guess for other operations.
+The default can be overridden by setting the
+.B metadata
+value for the
+.B CREATE
+keyword in
+.BR mdadm.conf .
+
+Options are:
+.RS
+.IP "0, 0.90, default"
+Use the original 0.90 format superblock. This format limits arrays to
+28 componenet devices and limits component devices of levels 1 and
+greater to 2 terabytes.
+.IP "1, 1.0, 1.1, 1.2"
+Use the new version-1 format superblock. This has few restrictions.
+The different subversion store the superblock at different locations
+on the device, either at the end (for 1.0), at the start (for 1.1) or
+4K from the start (for 1.2).
+.RE
.TP
-.BR --rounding=
-Specify rounding factor for linear array (==chunk size)
+.B --homehost=
+This will over-ride any
+.B HOMEHOST
+setting in the config file and provides the identify of the host which
+should be considered the home for any arrays.
-.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.
+When creating an array, the
+.B homehost
+will be recorded in the superblock. For version-1 superblocks, it will
+be prefixed to the array name. For version-0.90 superblocks part of
+the SHA1 hash of the hostname will be stored in the later half of the
+UUID.
-.TP
-.BR -p ", " --parity=
-Set raid5 parity algorithm. Options are:
-left-asymmetric,
-left-symmetric,
-right-asymmetric,
-right-symmetric,
-la, ra, ls, rs. The default is left-symmetric.
+When reporting information about an array, any array which is tagged
+for the given homehost will be reported as such.
-.TP
-.BR --layout=
-same as --parity
+When using Auto-Assemble, only arrays tagged for the given homehost
+will be assembled.
+
+.SH For create, build, or grow:
.TP
.BR -n ", " --raid-devices=
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.
+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=
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.
+number of 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 .
+The size can be given as
+.B max
+which means to choose the largest size that fits on all current drives.
+
+.TP
+.BR -c ", " --chunk=
+Specify chunk size of kibibytes. The default is 64.
+
+.TP
+.BR --rounding=
+Specify rounding factor for linear array (==chunk size)
+
+.TP
+.BR -l ", " --level=
+Set raid level. When used with
+.IR --create ,
+options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
+raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty. Obviously some of these are synonymous.
+
+When used with
+.IR --build ,
+only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
+
+Not yet supported with
+.IR --grow .
+
+.TP
+.BR -p ", " --layout=
+This option configures the fine details of data layout for raid5,
+and raid10 arrays, and controls the failure modes for
+.IR faulty .
+
+The layout of the raid5 parity block can be one of
+left-asymmetric,
+left-symmetric,
+right-asymmetric,
+right-symmetric,
+la, ra, ls, rs. The default is left-symmetric.
+
+When setting the failure mode for
+.I faulty
+the options are:
+write-transient,
+wt,
+read-transient,
+rt,
+write-persistent,
+wp,
+read-persistent,
+rp,
+write-all,
+read-fixable,
+rf,
+clear,
+flush,
+none.
+
+Each mode can be followed by a number which is used as a period
+between fault generation. Without a number, the fault is generated
+once on the first relevant request. With a number, the fault will be
+generated after that many request, and will continue to be generated
+every time the period elapses.
+
+Multiple failure modes can be current simultaneously by using the
+"--grow" option to set subsequent failure modes.
+
+"clear" or "none" will remove any pending or periodic failure modes,
+and "flush" will clear any persistent faults.
+
+To set the parity with "--grow", the level of the array ("faulty")
+must be specified before the fault mode is specified.
+
+Finally, the layout options for RAID10 are one of 'n', 'o' or 'p' followed
+by a small number. The default is 'n2'.
+
+.I n
+signals 'near' copies. Multiple copies of one data block are at
+similar offsets in different devices.
+
+.I o
+signals 'offset' copies. Rather than the chunks being duplicated
+within a stripe, whole stripes are duplicated but are rotated by one
+device so duplicate blocks are on different devices. Thus subsequent
+copies of a block are in the next drive, and are one chunk further
+down.
+
+.I f
+signals 'far' copies
+(multiple copies have very different offsets). See md(4) for more
+detail about 'near' and 'far'.
+
+The number is the number of copies of each datablock. 2 is normal, 3
+can be useful. This number can be at most equal to the number of
+devices in the array. It does not need to divide evenly into that
+number (e.g. it is perfectly legal to have an 'n2' layout for an array
+with an odd number of devices).
+
+.TP
+.BR --parity=
+same as --layout (thus explaining the p of
+.IR -p ).
+
+.TP
+.BR -b ", " --bitmap=
+Specify a file to store a write-intent bitmap in. The file should not
+exist unless --force is also given. The same file should be provided
+when assembling the array. If the word
+.B internal
+is given, then the bitmap is stored with the metadata on the array,
+and so is replicated on all devices. If the word
+.B none
+is given with
+.B --grow
+mode, then any bitmap that is present is removed.
+
+To help catch typing errors, the filename must contain at least one
+slash ('/') if it is a real file (not 'internal' or 'none').
+
+Note: external bitmaps are only known to work on ext2 and ext3.
+Storing bitmap files on other filesystems may result in serious problems.
+
+.TP
+.BR --bitmap-chunk=
+Set the chunksize of the bitmap. Each bit corresponds to that many
+Kilobytes of storage.
+When using a file based bitmap, the default is to use the smallest
+size that is atleast 4 and requires no more than 2^21 chunks.
+When using an
+.B internal
+bitmap, the chunksize is automatically determined to make best use of
+available space.
+
+
+.TP
+.BR -W ", " --write-mostly
+subsequent devices lists in a
+.BR --build ,
+.BR --create ,
+or
+.B --add
+command will be flagged as 'write-mostly'. This is valid for RAID1
+only and means that the 'md' driver will avoid reading from these
+devices if at all possible. This can be useful if mirroring over a
+slow link.
+
+.TP
+.BR --write-behind=
+Specify that write-behind mode should be enabled (valid for RAID1
+only). If an argument is specified, it will set the maximum number
+of outstanding writes allowed. The default value is 256.
+A write-intent bitmap is required in order to use write-behind
+mode, and write-behind is only attempted on drives marked as
+.IR write-mostly .
+
+.TP
+.BR --assume-clean
+Tell
+.I mdadm
+that the array pre-existed and is known to be clean. It can be useful
+when trying to recover from a major failure as you can be sure that no
+data will be affected unless you actually write to the array. It can
+also be used when creating a RAID1 or RAID10 if you want to avoid the
+initial resync, however this practice - while normally safe - is not
+recommended. Use this ony if you really know what you are doing.
+
+.TP
+.BR --backup-file=
+This is needed when --grow is used to increase the number of
+raid-devices in a RAID5 if there are no spare devices available.
+See the section below on RAID_DEVICE CHANGES. The file should be
+stored on a separate device, not on the raid array being reshaped.
+
+.TP
+.BR -N ", " --name=
+Set a
+.B name
+for the array. This is currently only effective when creating an
+array with a version-1 superblock. The name is a simple textual
+string that can be used to identify array components when assembling.
+
+.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, possibly allocating
+an unused minor number. "md" causes a non-partitionable array
+to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
+later) to be used. "yes" requires the named md device to have
+a 'standard' format, and the type and minor number will be determined
+from this. See DEVICE NAMES below.
+
+The argument can also come immediately after
+"-a". e.g. "-ap".
+
+If --auto is not given on the command line or in the config file, then
+the default will be
+.BR --auto=yes .
+
+If
+.I --scan
+is also given, then any
+.I auto=
+entries in the config file will over-ride the
+.I --auto
+instruction given on the command line.
+
+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 a 'p',
+and a number, e.g. "/dev/home1p3". If there is no
+trailing digit, then the partition names just have a number added,
+e.g. "/dev/scratch3".
+
+If the md device name is in a 'standard' format as described in DEVICE
+NAMES, then it will be created, if necessary, with the appropriate
+number based on that name. If the device name is not in one of these
+formats, then a unused minor number will be allocated. The minor
+number will be considered unused if there is no active array for that
+number, and there is no entry in /dev for that number and with a
+non-standard name.
+
+.TP
+.BR --symlink = no
+Normally when
+.B --auto
+causes
+.I mdadm
+to create devices in
+.B /dev/md/
+it will also create symlinks from
+.B /dev/
+with names starting with
+.B md
+or
+.BR md_ .
+Use
+.B --symlink=no
+to suppress this, or
+.B --symlink=yes
+to enforce this even if it is suppressing
+.IR mdadm.conf .
+
+
.SH For assemble:
.TP
.M --super-minor=dev
will look for super blocks with a minor number of 0.
+.TP
+.BR -N ", " --name=
+Specify the name of the array to assemble. This must be the name
+that was specified when creating the array. It must either match
+then name stored in the superblock exactly, or it must match
+with the current
+.I homehost
+is added to the start of the given name.
+
.TP
.BR -f ", " --force
Assemble the array even if some superblocks appear out-of-date
.TP
.BR -R ", " --run
-Attempt to start the array even if fewer drives were given than are
-needed for a full array. Normally if not all drives are found and
+Attempt to start the array even if fewer drives were given than were
+present last time the array was active. Normally if not all the
+expected drives are found and
.B --scan
is not used, then the array will be assembled but not started.
With
.B --run
an attempt will be made to start it anyway.
+.TP
+.B --no-degraded
+This is the reverse of
+.B --run
+in that it inhibits the started if array unless all expected drives
+are present. This is only needed with
+.B --scan
+and can be used if you physical connections to devices are
+not as reliable as you would like.
+
+.TP
+.BR -a ", " "--auto{=no,yes,md,mdp,part}"
+See this option under Create and Build options.
+
+.TP
+.BR -b ", " --bitmap=
+Specify the bitmap file that was given when the array was created. If
+an array has an
+.B internal
+bitmap, there is no need to specify this when assembling the array.
+
+.TP
+.BR --backup-file=
+If
+.B --backup-file
+was used to grow the number of raid-devices in a RAID5, and the system
+crashed during the critical section, then the same
+.B --backup-file
+must be presented to --assemble to allow possibly corrupted data to be
+restored.
+
.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 ,
+.BR uuid ,
+.BR name ,
+.BR homehost ,
+.BR resync ,
+.BR byteorder ,
+.BR devicesize ,
or
.BR super-minor .
The
.B sparc2.2
-option will adjust the superblock of an array what was created on a Sparc
+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"
The
.B super-minor
option will update the
-.B "prefered minor"
+.B "preferred 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.
+assembled.
+This can be useful if
+.B --examine
+reports a different "Preferred Minor" to
+.BR --detail .
+In some cases this update will be performed automatically
+by the kernel driver. In particular the update happens automatically
+at the first write to an array with redundancy (RAID level 1 or
+greater) on a 2.6 (or later) kernel.
+The
+.B uuid
+option will change the uuid of the array. If a UUID is given with the
+"--uuid" option that UUID will be used as a new UUID and will
+.B NOT
+be used to help identify the devices in the array.
+If no "--uuid" is given, a random uuid is chosen.
+
+The
+.B name
+option will change the
+.I name
+of the array as stored in the superblock. This is only supported for
+version-1 superblocks.
+
+The
+.B homehost
+option will change the
+.I homehost
+as recorded in the superblock. For version-0 superblocks, this is the
+same as updating the UUID.
+For version-1 superblocks, this involves updating the name.
+
+The
+.B resync
+option will cause the array to be marked
+.I dirty
+meaning that any redundancy in the array (e.g. parity for raid5,
+copies for raid1) may be incorrect. This will cause the raid system
+to perform a "resync" pass to make sure that all redundant information
+is correct.
+
+The
+.B byteorder
+option allows arrays to be moved between machines with different
+byte-order.
+When assembling such an array for the first time after a move, giving
+.B "--update=byteorder"
+will cause
+.I mdadm
+to expect superblocks to have their byteorder reversed, and will
+correct that order before assembling the array. This is only valid
+with original (Version 0.90) superblocks.
+
+The
+.B summaries
+option will correct the summaries in the superblock. That is the
+counts of total, working, active, failed, and spare devices.
+
+The
+.B devicesize
+will rarely be of use. It applies to version 1.1 and 1.2 metadata
+only (where the metadata is at the start of the device) and is only
+useful when the component device has changed size (typically become
+larger). The version 1 metadata records the amount of the device that
+can be used to store data, so if a device in a version 1.1 or 1.2
+array becomes larger, the metadata will still be visible, but the
+extra space will not. In this case it might be useful to assemble the
+array with
+.BR --update=devicesize .
+This will cause
+.I mdadm
+to determine the maximum usable amount of space on each device and
+update the relevant field in the metadata.
+
+.TP
+.B --auto-update-homehost
+This flag is only meaning with auto-assembly (see discussion below).
+In that situation, if no suitable arrays are found for this homehost,
+.I mdadm
+will recan for any arrays at all and will assemble them and update the
+homehost to match the current host.
.SH For Manage mode:
.TP
.BR -a ", " --add
-'''add, or
-hotadd listed devices.
+hot-add listed devices.
+
+.TP
+.BR --re-add
+re-add a device that was recently removed from an array.
.TP
.BR -r ", " --remove
.BR --set-faulty
same as --fail.
-.SH For Examine mode:
+.P
+Each of these options require that the first device list is the array
+to be acted upon and the remainder are component devices to be added,
+removed, or marked as fault. Several different operations can be
+specified for different devices, e.g.
+.in +5
+mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
+.in -5
+Each operation applies to all devices listed until the next
+operations.
+
+If an array is using a write-intent bitmap, then devices which have
+been removed can be re-added in a way that avoids a full
+reconstruction but instead just updated the blocks that have changed
+since the device was removed. For arrays with persistent metadata
+(superblocks) this is done automatically. For arrays created with
+.B --build
+mdadm needs to be told that this device we removed recently with
+.B --re-add.
+
+Devices can only be removed from an array if they are not in active
+use. i.e. that must be spares or failed devices. To remove an active
+device, it must be marked as
+.B faulty
+first.
+
+.SH For Misc mode:
+
+.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 -E ", " --examine
+Print content of md superblock on device(s).
.TP
.B --sparc2.2
-In an array was created on a 2.2 Linux kernel patched with RAID
+If 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
the right thing, then the array can be successfully assembled using
.BR "--assemble --update=sparc2.2" .
-.SH For Misc mode:
+.TP
+.BR -X ", " --examine-bitmap
+Report information about a bitmap file.
.TP
.BR -R ", " --run
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
.BR -p ", " --program ", " --alert
Give a program to be run whenever an event is detected.
+.TP
+.BR -y ", " --syslog
+Cause all events to be reported through 'syslog'. The messages have
+facility of 'daemon' and varying priorities.
+
.TP
.BR -d ", " --delay
Give a delay in seconds.
which will only continue monitoring if a mail address or alert program
is found in the config file.
+.TP
+.BR -i ", " --pid-file
+When
+.B mdadm
+is running in daemon mode, write the pid of the daemon process to
+the specified file, instead of printing it on standard output.
+
+.TP
+.BR -1 ", " --oneshot
+Check arrays only once. This will generate
+.B NewArray
+events and more significantly
+.B DegradedArray
+and
+.B SparesMissing
+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 do get through successfully.
+
.SH ASSEMBLE MODE
.HP 12
If precisely one device is listed, but
.B --scan
-is not given, that
+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
+The identity can be given with the
.B --uuid
option, with the
.B --super-minor
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
+Devices can be given on the
.B --assemble
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
+The config file is only used if explicitly named with
.B --config
or requested with (a possibly implicit)
-.B --scan.
+.B --scan.
In the later case,
.B /etc/mdadm.conf
is used.
-If
+If
.B --scan
is not given, then the config file will only be used to find the
identity of md arrays.
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, 6, or 10), give the
.B --run
flag.
+If the md device does not exist, then it will be created providing the
+intent is clear. i.e. the name must be in a standard form, or the
+.I --auto
+option must be given to clarify how and whether the device should be
+created.
+
+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 in use, 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.
+
+.SS Auto Assembly
+When
+.B --assemble
+is used with
+.B --scan
+and no devices are listed,
+.I mdadm
+will first attempt to assemble all the arrays listed in the config
+file.
+
+If a
+.B homehost
+has been specified (either in the config file or on the command line),
+.I mdadm
+will look further for possible arrays and will try to assemble
+anything that it finds which is tagged as belonging to the given
+homehost. This is the only situation where
+.I mdadm
+will assemble arrays without being given specific device name or
+identify information for the array.
+
+If
+.I mdadm
+finds a consistent set of devices that look like they should comprise
+an array, and if the superblock is tagged as belonging to the given
+home host, it will automatically choose a device name and try to
+assemble the array. If the array uses version-0.90 metadata, then the
+.B minor
+number as recorded in the superblock is used to create a name in
+.B /dev/md/
+so for example
+.BR /dev/md/3 .
+If the array uses version-1 metadata, then the
+.B name
+from the superblock is used to similarly create a name in
+.BR /dev/md .
+The name will have any 'host' prefix stripped first.
+
+If
+.I mdadm
+cannot find any array for the given host at all, and if
+.B --auto-update-homehost
+is given, then
+.I mdadm
+will search again for any array (not just an array created for this
+host) and will assemble each assuming
+.IR --update=homehost .
+This will change the host tag in the superblock so that on the next run,
+these arrays will be found without the second pass. The intention of
+this feature is to support transitioning a set of md arrays to using
+homehost tagging.
+
+The reason for requiring arrays to be tagged with the homehost for
+auto assembly is to guard against problems that can arise when moving
+devices from one host to another.
.SH BUILD MODE
.I devices
.PP
-This usage is similar to
+This usage is similar to
.BR --create .
-The difference is that it creates a legacy array without a superblock. With
+The difference is that it creates an array without a superblock. With
these arrays there is no difference between initially creating the array and
subsequently assembling the array, except that hopefully there is useful
data there in the second case.
-The level may only be 0, raid0, or linear. All devices must be listed
-and the array will be started once complete.
+The level may raid0, linear, multipath, or faulty, or one of their
+synonyms. All devices must be listed and the array will be started
+once complete.
.SH CREATE MODE
This usage will initialise a new md array, associate some devices with
it, and activate the array.
+If 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%.
If any discrepancy is found, the array will not automatically be run, though
-the presence of a
+the presence of a
.B --run
can override this caution.
.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".
+"\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
"\fBmissing\fP".
-'''If the
+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.
+
+When creating an array with version-1 metadata a name for the host is
+required.
+If this is not given with the
+.B --name
+option,
+.I mdadm
+will chose a name based on the last component of the name of the
+device being created. So if
+.B /dev/md3
+is being created, then the name
+.B 3
+will be chosen.
+If
+.B /dev/md/home
+is being created, then the name
+.B home
+will be used.
+
+'''If the
'''.B --size
'''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 --run.
+'''If no
'''.B --size
'''is given, the apparent size of the smallest drive given is used.
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
.B --readonly
start the array readonly - not supported yet.
+
.SH MANAGE MODE
.HP 12
Usage:
.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.
+command.
.SH MISC MODE
.HP 12
.I devices ...
.PP
-MISC mode includes a number if distinct operations that
+MISC mode includes a number of distinct operations that
operate on distinct devices. The operations are:
.TP
--query
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
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.
+and if the destination array has a failed drive but no spares.
If any devices are listed on the command line,
.B mdadm
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
+and is given 2 or 3 command-line arguments. 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.
.TP
.B DeviceDisappeared
An md array which previously was configured appears to no longer be
-configured.
+configured. (syslog priority: Critical)
+
+If
+.I mdadm
+was told to monitor an array which is RAID0 or Linear, then it will
+report
+.B DeviceDisappeared
+with the extra information
+.BR Wrong-Level .
+This is because RAID0 and Linear do not support the device-failed,
+hot-spare and resync operations which are monitored.
.TP
.B RebuildStarted
-An md array started reconstruction.
+An md array started reconstruction. (syslog priority: Warning)
.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.
+percentage of the total. (syslog priority: Warning)
+
+.TP
+.B RebuildFinished
+An md array that was rebuilding, isn't any more, either because it
+finished normally or was aborted. (syslog priority: Warning)
.TP
.B Fail
-An active component device of an array has been marked as faulty.
+An active component device of an array has been marked as
+faulty. (syslog priority: Critical)
.TP
.B FailSpare
A spare component device which was being rebuilt to replace a faulty
-device has failed.
+device has failed. (syslog priority: Critial)
.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.
+device has been successfully rebuilt and has been made active.
+(syslog priority: Info)
.TP
.B NewArray
A new md array has been detected in the
.B /proc/mdstat
-file.
+file. (syslog priority: Info)
+
+.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.
+(syslog priority: Critial)
.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.
+(syslog priority: Info)
+.TP
+.B SparesMissing
+If
+.I mdadm
+has been told, via the config file, that an array should have a certain
+number of spare devices, and
+.I mdadm
+detects that it has fewer that this number when it first sees the
+array, it will report a
+.B SparesMissing
+message.
+(syslog priority: Warning)
+
+.TP
+.B TestMessage
+An array was found at startup, and the
+.B --test
+flag was given.
+(syslog priority: Info)
.RE
Only
-.B Fail
+.B Fail ,
+.B FailSpare ,
+.B DegradedArray ,
+.B SparesMissing ,
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 are being added during 2.6 development,
+including restructuring a raid5 array to have more active devices.
+
+Currently the only support available is to
+.IP \(bu 4
+change the "size" attribute
+for RAID1, RAID5 and RAID6.
+.IP \(bu 4
+increase the "raid-disks" attribute of RAID1 and RAID5.
+.IP \(bu 4
+add a write-intent bitmap to any array which support these bitmaps, or
+remove a write-intent bitmap from such an array.
+.PP
+
+.SS SIZE CHANGES
+Normally when an array is built 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.
+
+.SS RAID-DEVICES CHANGES
+
+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 will be activated immediately.
+
+Increasing the number of active devices in a RAID5 is much more
+effort. Every block in the array will need to be read and written
+back to a new location. From 2.6.17, the Linux Kernel is able to do
+this safely, including restart and interrupted "reshape".
+
+When relocating the first few stripes on a raid5, it is not possible
+to keep the data on disk completely consistent and crash-proof. To
+provide the required safety, mdadm disables writes to the array while
+this "critical section" is reshaped, and takes a backup of the data
+that is in that section. This backup is normally stored in any spare
+devices that the array has, however it can also be stored in a
+separate file specified with the
+.B --backup-file
+option. If this option is used, and the system does crash during the
+critical period, the same file must be passed to
+.B --assemble
+to restore the backup and reassemble the array.
+
+.SS BITMAP CHANGES
+
+A write-intent bitmap can be added to, or removed from, an active
+array. Either internal bitmaps, or bitmaps stored in a separate file
+can be added. Note that if you add a bitmap stored in a file which is
+in a filesystem that is on the raid array being affected, the system
+will deadlock. The bitmap must be on a separate filesystem.
+
.SH EXAMPLES
.B " mdadm --query /dev/name-of-device"
.B " mdadm --assemble --scan"
.br
-This will assemble and start all arrays listed in the standard confile
+This will assemble and start all arrays listed in the standard config file
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.
+currently in use). This will typically go in a system shutdown script.
.B " mdadm --follow --scan --delay=120"
.br
.br
.B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
.ber
-This will find what arrays could be assembled from existign IDE and
+This will find what arrays could be assembled from existing 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
.B " mdadm --create --help"
.br
-Providew help about the Create mode.
+Provide help about the Create mode.
.B " mdadm --config --help"
.br
.SS /proc/mdstat
-If you're using the
-.B /proc
+If you're using the
+.B /proc
filesystem,
.B /proc/mdstat
lists all active md devices with information about them.
.BR mdadm.conf (5)
for more details.
+.SH DEVICE NAMES
+
+While entries in the /dev directory can have any format you like,
+.I mdadm
+has an understanding of 'standard' formats which it uses to guide its
+behaviour when creating device files via the
+.I --auto
+option.
+
+The standard names for non-partitioned arrays (the only sort of md
+array available in 2.4 and earlier) either of
+.IP
+/dev/mdNN
+.br
+/dev/md/NN
+.PP
+where NN is a number.
+The standard names for partitionable arrays (as available from 2.6
+onwards) is one of
+.IP
+/dev/md/dNN
+.br
+/dev/md_dNN
+.PP
+Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
.SH NOTE
.B mdadm
was previously known as
.BR mdctl .
-
+.P
+.B mdadm
+is completely separate from the
+.B raidtools
+package, and does not use the
+.I /etc/raidtab
+configuration file at all.
+
.SH SEE ALSO
For information on the various levels of
RAID, check out:
.UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
.UE
+'''.PP
+'''for new releases of the RAID driver check out:
+'''
+'''.IP
+'''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
+'''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
+'''.UE
+'''.PP
+'''or
+'''.IP
+'''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
+'''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
+'''.UE
.PP
-for new releases of the RAID driver check out:
-
+The latest version of
+.I mdadm
+should always be available from
.IP
-.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
-ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
+.UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
+http://www.kernel.org/pub/linux/utils/raid/mdadm/
.UE
.PP
-or
-.IP
-.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
-http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
-.URk
-.PP
-.BR mdadm.conf (5),
-.BR md (4).
+.IR mdadm.conf (5),
+.IR md (4).
.PP
.IR raidtab (5),
.IR raid0run (8),
.IR raidstop (8),
-.IR mkraid (8)
+.IR mkraid (8).
projects / thirdparty / mdadm.git / blobdiff