.\" -*- nroff -*-
-.TH MDADM 8
+.\" 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 "" v2.6.5
.SH NAME
mdadm \- manage MD devices
.I aka
-Linux Software Raid.
+Linux Software RAID
.SH SYNOPSIS
.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
+drives or partitions thereof) 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 ,
+.BR RAID6 ,
+.BR RAID10 ,
+.BR MULTIPATH ,
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 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. Also 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.
+.BR FAULTY .
+
+.B MULTIPATH
+is not a Software RAID mechanism, but does involve
+multiple devices:
+each device is a path to one common physical storage device.
+
+.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 several major modes of operation:
.TP
.B Assemble
-Assemble the parts of a previously created
+Assemble the components 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
+components 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
Create a new array with per-device superblocks.
-'''It can progress
-'''in several step create-add-add-run or it can all happen with one command.
+.\"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 and changing the number of active devices in RAID
+levels 1/4/5/6, as well as adding or removing a write-intent bitmap.
+
+.TP
+.B "Incremental Assembly"
+Add a single device to an appropriate array. If the addition of the
+device makes the array runnable, the array will be started.
+This provides a convenient interface to a
+.I hot-plug
+system. As each device is detected,
+.I mdadm
+has a chance to include it in some array as appropriate.
.TP
.B Manage
.TP
.B Misc
-This mode allows operations on independent devices such as examine MD
-superblocks, erasing old superblocks and stopping active arrays.
+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.
.TP
-.B "Follow or Monitor"
-Monitor one or more md devices and act on any state changes.
-
+.B Auto-detect
+This mode does not act on a specific device or array, but rather it
+requests the Linux Kernel to activate any auto-detected arrays.
.SH OPTIONS
-Available options are:
+.SH Options for selecting a mode are:
.TP
-.BR -A ", " --assemble
-Assemble an existing array.
+.BR \-A ", " \-\-assemble
+Assemble a pre-existing array.
.TP
-.BR -B ", " --build
+.BR \-B ", " \-\-build
Build a legacy array without superblocks.
.TP
-.BR -C ", " --create
+.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.
+.BR \-F ", " \-\-follow ", " \-\-monitor
+Select
+.B Monitor
+mode.
.TP
-.BR -D ", " --detail
-Print detail of one or more md devices.
+.BR \-G ", " \-\-grow
+Change the size or shape of an active array.
.TP
-.BR -E ", " --examine
-Print content of md superblock on device(s).
+.BR \-I ", " \-\-incremental
+Add a single device into an appropriate array, and possibly start the array.
.TP
-.BR -F ", " --follow ", " --monitor
-Select
-.B Monitor
-mode.
+.B \-\-auto-detect
+Request that the kernel starts any auto-detected arrays. This can only
+work if
+.I md
+is compiled into the kernel \(em not if it is a module.
+Arrays can be auto-detected by the kernel if all the components are in
+primary MS-DOS partitions with partition type
+.BR FD .
+In-kernel autodetect is not recommended for new installations. Using
+.I mdadm
+to detect and assemble arrays \(em possibly in an
+.I initrd
+\(em is substantially more flexible and should be preferred.
+
+.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 general help message or, after one of the above options, a
+mode-specific help message.
.TP
-.BR -h ", " --help
-Display help message or, after above option, mode specific help message.
+.B \-\-help\-options
+Display more detailed help about command line parsing and some commonly
+used options.
.TP
-.BR -V ", " --version
+.BR \-V ", " \-\-version
Print version information for mdadm.
.TP
-.BR -v ", " --verbose
-Be more verbose about what is happening.
+.BR \-v ", " \-\-verbose
+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
+.BR \-b ", " \-\-brief
Be less verbose. This is used with
-.B --detail
+.B \-\-detail
and
-.BR --examine .
+.BR \-\-examine .
+Using
+.B \-\-brief
+with
+.B \-\-verbose
+gives an intermediate level of verbosity.
.TP
-.BR -f ", " --force
-Be more forceful about certain operations. See the various modes of
+.BR \-f ", " \-\-force
+Be more forceful about certain operations. See the various modes for
the exact meaning of this option in different contexts.
.TP
-.BR -c ", " --config=
-Specify the config file. Default is
-.BR /etc/mdadm.conf .
+.BR \-c ", " \-\-config=
+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
+.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
+.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
+permission to get any missing information (like component devices,
+array devices, array identities, and alert destination) from the
+configuration file (see previous option);
+one exception is MISC mode when using
+.B \-\-detail
or
-.B --stop
+.B \-\-stop,
in which case
-.B --scan
+.B \-\-scan
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
+.BR \-\-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 component 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 sub-versions 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 override any
+.B HOMEHOST
+setting in the config file and provides the identity 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,right}-{,a}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-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 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, RAID5 and RAID6 arrays, and only on kernels which provide
+necessary support.
.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=
-Amount (in Kibibytes) of space to use from each drive in RAID1/4/5.
+.BR \-z ", " \-\-size=
+Amount (in Kibibytes) of space to use from each drive in RAID level 1/4/5/6.
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
+.BR \-\-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
+.BR \-\-build ,
+only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
+
+Not yet supported with
+.BR \-\-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
+.BR left\-asymmetric ,
+.BR left\-symmetric ,
+.BR right\-asymmetric ,
+.BR right\-symmetric ,
+.BR la ", " ra ", " ls ", " rs .
+The default is
+.BR left\-symmetric .
+
+When setting the failure mode for level
+.I faulty,
+the options are:
+.BR write\-transient ", " wt ,
+.BR read\-transient ", " rt ,
+.BR write\-persistent ", " wp ,
+.BR read\-persistent ", " rp ,
+.BR write\-all ,
+.BR read\-fixable ", " rf ,
+.BR clear ", " flush ", " none .
+
+Each failure 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 requests, and will continue to be generated
+every time the period elapses.
+
+Multiple failure modes can be current simultaneously by using the
+.B \-\-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
+.BR \-\-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 'f' followed
+by a small number. The default is 'n2'. The supported options are:
+
+.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
+.B \-\-layout
+(thus explaining the p of
+.BR \-p ).
+
+.TP
+.BR \-b ", " \-\-bitmap=
+Specify a file to store a write-intent bitmap in. The file should not
+exist unless
+.B \-\-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 at-least 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 \(em while normally safe \(em is not
+recommended. Use this only if you really know what you are doing.
+
+.TP
+.BR \-\-backup\-file=
+This is needed when
+.B \-\-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
+.B \-\-auto
+is not given on the command line or in the config file, then
+the default will be
+.BR \-\-auto=yes .
+
+If
+.B \-\-scan
+is also given, then any
+.I auto=
+entries in the config file will override the
+.B \-\-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
-.BR -u ", " --uuid=
+.BR \-u ", " \-\-uuid=
uuid of array to assemble. Devices which don't have this uuid are
excluded
.TP
-.BR -m ", " --super-minor=
+.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
+.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
+the name stored in the superblock exactly, or it must match
+with the current
+.I homehost
+prefixed 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
-.B --scan
+.BR \-R ", " \-\-run
+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
+.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 startup of array unless all expected drives
+are present. This is only needed with
+.B \-\-scan,
+and can be used if the 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
+.B \-\-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 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
+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 "preferred minor"
+field on each superblock to match the minor number of the array being
+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
+.B \-\-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
+.B \-\-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 meaningful with auto-assembly (see discussion below).
+In that situation, if no suitable arrays are found for this homehost,
+.I mdadm
+will rescan 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.
+.BR \-a ", " \-\-add
+hot-add listed devices.
.TP
-.BR -r ", " --remove
-remove listed devices. The must not be active. i.e. they should
-be failed or spare devices.
+.BR \-\-re\-add
+re-add a device that was recently removed from an array.
.TP
-.BR -f ", " --fail
+.BR \-r ", " \-\-remove
+remove listed devices. They must not be active. i.e. they should
+be failed or spare devices. As well as the name of a device file
+(e.g.
+.BR /dev/sda1 )
+the words
+.B failed
+and
+.B detached
+can be given to
+.BR \-\-remove .
+The first causes all failed device to be removed. The second causes
+any device which is no longer connected to the system (i.e an 'open'
+returns
+.BR ENXIO )
+to be removed. This will only succeed for devices that are spares or
+have already been marked as failed.
+
+.TP
+.BR \-f ", " \-\-fail
mark listed devices as faulty.
+As well as the name of a device file, the word
+.B detached
+can be given. This will cause any device that has been detached from
+the system to be marked as failed. It can then be removed.
.TP
-.BR --set-faulty
-same as --fail.
+.BR \-\-set\-faulty
+same as
+.BR \-\-fail .
+
+.P
+Each of these options require that the first device listed is the array
+to be acted upon, and the remainder are component devices to be added,
+removed, or marked as faulty. 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
+operation.
+
+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 updates 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
+.BR \-\-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 first be marked as
+.B faulty.
.SH For Misc mode:
.TP
-.BR -R ", " --run
+.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 \-Y ", " \-\-export
+When used with
+.B \-\-detail
+or
+.BR \-\-examine ,
+output will be formatted as
+.B key=value
+pairs for easy import into the environment.
+
+.TP
+.BR \-E ", " \-\-examine
+Print content of md superblock on device(s).
+.TP
+.B \-\-sparc2.2
+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
+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" .
+
+.TP
+.BR \-X ", " \-\-examine\-bitmap
+Report information about a bitmap file.
+The argument is either an external bitmap file or an array component
+in case of an internal bitmap.
+
+.TP
+.BR \-R ", " \-\-run
start a partially built array.
.TP
-.BR -S ", " --stop
+.BR \-S ", " \-\-stop
deactivate array, releasing all resources.
.TP
-.BR -o ", " --readonly
+.BR \-o ", " \-\-readonly
mark array as readonly.
.TP
-.BR -w ", " --readwrite
+.BR \-w ", " \-\-readwrite
mark array as readwrite.
.TP
-.B --zero-superblock
+.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
+overwritten with zeros. With
+.B \-\-force
+the block where the superblock would be is overwritten 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.
+
+.TP
+.BR \-W ", " \-\-wait
+For each md device given, wait for any resync, recovery, or reshape
+activity to finish before returning.
+.I mdadm
+will return with success if it actually waited for every device
+listed, otherwise it will return failure.
+
+.SH For Incremental Assembly mode:
+.TP
+.BR \-\-rebuild\-map ", " \-r
+Rebuild the map file
+.RB ( /var/run/mdadm/map )
+that
+.I mdadm
+uses to help track which arrays are currently being assembled.
+
+.TP
+.BR \-\-run ", " \-R
+Run any array assembled as soon as a minimal number of devices are
+available, rather than waiting until all expected devices are present.
+
+.TP
+.BR \-\-scan ", " \-s
+Only meaningful with
+.B \-R
+this will scan the
+.B map
+file for arrays that are being incrementally assembled and will try to
+start any that are not already started. If any such array is listed
+in
+.B mdadm.conf
+as requiring an external bitmap, that bitmap will be attached first.
+
.SH For Monitor mode:
.TP
-.BR -m ", " --mail
+.BR \-m ", " \-\-mail
Give a mail address to send alerts to.
.TP
-.BR -p ", " --program ", " --alert
+.BR \-p ", " \-\-program ", " \-\-alert
Give a program to be run whenever an event is detected.
.TP
-.BR -d ", " --delay
+.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.
.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.
+
+.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
Usage:
-.B mdadm --assemble
-.I device options...
+.B mdadm \-\-assemble
+.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
+.B mdadm \-\-assemble \-\-scan
.I options...
.PP
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
-.B --scan
-or is found from the config file. In the latter case, multiple md devices
-can be started with a single mdadm command.
-
-The identity can be given with the
-.B --uuid
+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, then
+.I mdadm
+acts as though
+.B \-\-scan
+was given and identity 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 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.
-
-The config file is only used if explicitly named with
-.B --config
-or requested with
-.B --scan.
+.B \-\-super\-minor
+option, will be taken from the md-device record in the config file, or
+will be taken from the super block of the first component-device
+listed on the command line.
+
+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
+.B \-\-config
+or requested with (a possibly implicit)
+.BR \-\-scan .
In the later case,
.B /etc/mdadm.conf
is used.
-If
-.B --scan
+If
+.B \-\-scan
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
-.B --scan
-is not given and insufficient drives were lists to start a complete
+Normally the array will be started after it is assembled. However if
+.B \-\-scan
+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
-.B --run
+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
+.B \-\-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 \(em 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 option "auto" 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
+identity 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
+.BR \-\-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
.HP 12
Usage:
-.B mdadm --build
-.I device
-.BI --chunk= X
-.BI --level= Y
-.BI --raid-disks= Z
+.B mdadm \-\-build
+.I md-device
+.BI \-\-chunk= X
+.BI \-\-level= Y
+.BI \-\-raid\-devices= Z
.I devices
.PP
-This usage is similar to
-.BR --create .
-The difference is that it creates a legacy array without a superblock. With
+This usage is similar to
+.BR \-\-create .
+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
.HP 12
Usage:
-.B mdadm --create
-.I device
-.BI --chunk= X
-.BI --level= Y
+.B mdadm \-\-create
+.I md-device
+.BI \-\-chunk= X
+.BI \-\-level= Y
.br
-.BI --raid-disks= Z
+.BI \-\-raid\-devices= Z
.I devices
.PP
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 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
-the presence of a
-.B --run
+the presence of a
+.B \-\-run
can override this caution.
-'''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 --size
-'''is given, the apparent size of the smallest drive given is used.
-
-The General Management options that are valid with --create are:
+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 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".
+
+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 overridden with the
+.B \-\-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.
+
+A new array will normally get a randomly assigned 128bit UUID which is
+very likely to be unique. If you have a specific need, you can choose
+a UUID for the array by giving the
+.B \-\-uuid=
+option. Be warned that creating two arrays with the same UUID is a
+recipe for disaster. Also, using
+.B \-\-uuid=
+when creating a v0.90 array will silently override any
+.B \-\-homehost=
+setting.
+.\"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 \-\-size
+.\"is given, the apparent size of the smallest drive given is used.
+
+The General Management options that are valid with
+.B \-\-create
+are:
.TP
-.B --run
-insist of running the array even if some devices look like they might
+.B \-\-run
+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.
+.B \-\-readonly
+start the array readonly \(em not supported yet.
+
.SH MANAGE MODE
.HP 12
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
-command.
+in as a spare. However only one md array can be affected by a single
+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
+.B \-\-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. mdadm will display
-a detailed description of the array.
-.B --brief
-will cause the output to be less detailed and format to be
+.B \-\-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 .
+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 such that it is unusable.
+.TP
+4
+There was an error while trying to get information about the device.
+.RE
.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.
+.B \-\-examine
+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
-.B --scan
-then multiple devices that are components of the one array
+.B \-\-brief
+or
+.B \-\-scan
+is given, 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 .
-Have
-.B --scan
+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.
+.B \-\-stop
+The devices should be active md arrays which will be deactivated, as
+long as they are not currently in use.
.TP
---run
+.B \-\-run
This will fully activate a partially assembled md array.
.TP
---readonly
+.B \-\-readonly
This will mark an active array as read-only, providing that it is
not currently being used.
.TP
---readwrite
+.B \-\-readwrite
This will change a
.B readonly
array back to being read/write.
+.TP
+.B \-\-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 --monitor
+.B mdadm \-\-monitor
.I options... devices...
.PP
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 no 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
+.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 (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 events to a program, the program is run once for each event,
+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).
If
-.B --scan
+.B \-\-scan
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
+.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
-configured.
+An md array which previously was configured appears to no longer be
+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: Critical)
.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: Critical)
.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 than 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
+The program is run with two or three arguments: the event
name, the array device and possibly a second device.
Each event has an associated array device (e.g.
For
.B mdadm
to move spares from one array to another, the different arrays need to
-be labelled with the same
+be labeled 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 name.
+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
+detects that an array 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
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, RAID5, and RAID6.
+.IP \(bu 4
+add a write-intent bitmap to any array which supports 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 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 INCREMENTAL MODE
+
+.HP 12
+Usage:
+.B mdadm \-\-incremental
+.RB [ \-\-run ]
+.RB [ \-\-quiet ]
+.I component-device
+.HP 12
+Usage:
+.B mdadm \-\-incremental \-\-rebuild
+.HP 12
+Usage:
+.B mdadm \-\-incremental \-\-run \-\-scan
+
+
+.PP
+This mode is designed to be used in conjunction with a device
+discovery system. As devices are found in a system, they can be
+passed to
+.B "mdadm \-\-incremental"
+to be conditionally added to an appropriate array.
+
+.I mdadm
+performs a number of tests to determine if the device is part of an
+array, and which array it should be part of. If an appropriate array
+is found, or can be created,
+.I mdadm
+adds the device to the array and conditionally starts the array.
+
+Note that
+.I mdadm
+will only add devices to an array which were previously working
+(active or spare) parts of that array. It does not currently support
+automatic inclusion of a new drive as a spare in some array.
+
+.B "mdadm \-\-incremental"
+requires a bug-fix in all kernels through 2.6.19.
+Hopefully, this will be fixed in 2.6.20; alternately, apply the patch
+which is included with the mdadm source distribution. If
+.I mdadm
+detects that this bug is present, it will abort any attempt to use
+.BR \-\-incremental .
+
+The tests that
+.I mdadm
+makes are as follow:
+.IP +
+Is the device permitted by
+.BR mdadm.conf ?
+That is, is it listed in a
+.B DEVICES
+line in that file. If
+.B DEVICES
+is absent then the default it to allow any device. Similar if
+.B DEVICES
+contains the special word
+.B partitions
+then any device is allowed. Otherwise the device name given to
+.I mdadm
+must match one of the names or patterns in a
+.B DEVICES
+line.
+
+.IP +
+Does the device have a valid md superblock. If a specific metadata
+version is request with
+.B \-\-metadata
+or
+.B \-e
+then only that style of metadata is accepted, otherwise
+.I mdadm
+finds any known version of metadata. If no
+.I md
+metadata is found, the device is rejected.
+
+.IP +
+Does the metadata match an expected array?
+The metadata can match in two ways. Either there is an array listed
+in
+.B mdadm.conf
+which identifies the array (either by UUID, by name, by device list,
+or by minor-number), or the array was created with a
+.B homehost
+specified and that
+.B homehost
+matches the one in
+.B mdadm.conf
+or on the command line.
+If
+.I mdadm
+is not able to positively identify the array as belonging to the
+current host, the device will be rejected.
+
+.IP +
+.I mdadm
+keeps a list of arrays that it has partially assembled in
+.B /var/run/mdadm/map
+(or
+.B /var/run/mdadm.map
+if the directory doesn't exist). If no array exists which matches
+the metadata on the new device,
+.I mdadm
+must choose a device name and unit number. It does this based on any
+name given in
+.B mdadm.conf
+or any name information stored in the metadata. If this name
+suggests a unit number, that number will be used, otherwise a free
+unit number will be chosen. Normally
+.I mdadm
+will prefer to create a partitionable array, however if the
+.B CREATE
+line in
+.B mdadm.conf
+suggests that a non-partitionable array is preferred, that will be
+honoured.
+
+.IP +
+Once an appropriate array is found or created and the device is added,
+.I mdadm
+must decide if the array is ready to be started. It will
+normally compare the number of available (non-spare) devices to the
+number of devices that the metadata suggests need to be active. If
+there are at least that many, the array will be started. This means
+that if any devices are missing the array will not be restarted.
+
+As an alternative,
+.B \-\-run
+may be passed to
+.B mdadm
+in which case the array will be run as soon as there are enough
+devices present for the data to be accessible. For a raid1, that
+means one device will start the array. For a clean raid5, the array
+will be started as soon as all but one drive is present.
+
+Note that neither of these approaches is really ideal. If it can
+be known that all device discovery has completed, then
+.br
+.B " mdadm \-IRs"
+.br
+can be run which will try to start all arrays that are being
+incrementally assembled. They are started in "read-auto" mode in
+which they are read-only until the first write request. This means
+that no metadata updates are made and no attempt at resync or recovery
+happens. Further devices that are found before the first write can
+still be added safely.
+
+.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 config
+file. This command will typically go in a system startup file.
+
+.B " mdadm \-\-stop \-\-scan"
+.br
+This will shut down all arrays that can be shut down (i.e. are not
+currently in use). This will typically go 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"
+.br
+This will find arrays which could be assembled from existing IDE and
+SCSI whole drives (not partitions), and store the information in 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 were 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 \-Iq /dev/somedevice"
+.br
+Try to incorporate newly discovered device into some array as
+appropriate.
+
+.B " mdadm \-\-incremental \-\-rebuild \-\-run \-\-scan"
+.br
+Rebuild the array map from any current arrays, and then start any that
+can be started.
+
+.B " mdadm /dev/md4 --fail detached --remove detached"
+.br
+Any devices which are components of /dev/md4 will be marked as faulty
+and then remove from the array.
+
+.B " mdadm \-\-create \-\-help"
+.br
+Provide 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
.SS /proc/mdstat
-If you're using the
-.B /proc
+If you're using the
+.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
.BR mdadm.conf (5)
for more details.
+.SS /var/run/mdadm/map
+When
+.B \-\-incremental
+mode is used, this file gets a list of arrays currently being created.
+If
+.B /var/run/mdadm
+does not exist as a directory, then
+.B /var/run/mdadm.map
+is used instead.
+
+.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
+.B \-\-auto
+option.
+
+The standard names for non-partitioned arrays (the only sort of md
+array available in 2.4 and earlier) are 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) are either 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 TODO
-
-Finish and document Follow mode.
+.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:
+For further information on MD and the various levels of
+RAID, see:
.IP
-.UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
-http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
+.UR http://unthought.net/Software-RAID.HOWTO/
+http://unthought.net/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
+.UR http://linux-raid.osdl.org/
+http://linux\-raid.osdl.org/
.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
-or
+The latest version of
+.I mdadm
+should always be available from
.IP
-.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
-http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
-.URk
+.UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
+http://www.kernel.org/pub/linux/utils/raid/mdadm/
+.UE
.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