.\" -*- nroff -*-
-''' 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
+.\" 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 "" v3.1.2
.SH NAME
mdadm \- manage MD devices
.I aka
-Linux Software Raid.
+Linux Software RAID
.SH SYNOPSIS
.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
+real block devices. This allows multiple devices (typically disk
+drives or partitions thereof) to be combined into a single device to
hold (for example) a single filesystem.
Some RAID levels include redundancy and so can survive some degree of
device failure.
.BR RAID6 ,
.BR RAID10 ,
.BR MULTIPATH ,
+.BR FAULTY ,
and
-.BR FAULTY .
+.BR CONTAINER .
.B MULTIPATH
is not a Software RAID mechanism, but does involve
-multiple devices. For
-.B MULTIPATH
+multiple devices:
each device is a path to one common physical storage device.
+New installations should not use md/multipath as it is not well
+supported and has no ongoing development. Use the Device Mapper based
+multipath-tools instead.
.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.
+.B CONTAINER
+is different again. A
+.B CONTAINER
+is a collection of devices that are
+managed as a set. This is similar to the set of devices connected to
+a hardware RAID controller. The set of devices may contain a number
+of different RAID arrays each utilising some (or all) of the blocks from a
+number of the devices in the set. For example, two devices in a 5-device set
+might form a RAID1 using the whole devices. The remaining three might
+have a RAID5 over the first half of each device, and a RAID0 over the
+second half.
+
+With a
+.BR CONTAINER ,
+there is one set of metadata that describes all of
+the arrays in the container. So when
+.I mdadm
+creates a
+.B CONTAINER
+device, the device just represents the metadata. Other normal arrays (RAID1
+etc) can be created inside the container.
.SH MODES
-mdadm has 7 major modes of operation:
+mdadm has several major modes of operation:
.TP
.B Assemble
-Assemble the parts of a previously created
-array into an active array. Components can be explicitly given
+Assemble the components of a previously created
+array into an active array. Components can be explicitly given
or can be searched for.
-.B mdadm
+.I mdadm
checks that the components
do form a bona fide array, and can, on request, fiddle superblock
information so as to assemble a faulty array.
.TP
.B Build
-Build an array that doesn't have per-device superblocks. For these
+Build an array that doesn't have per-device metadata (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
+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.
+Create a new array with per-device metadata (superblocks).
+Appropriate metadata is written to each device, and then the array
+comprising those devices is activated. A 'resync' process is started
+to make sure that the array is consistent (e.g. both sides of a mirror
+contain the same data) but the content of the device is left otherwise
+untouched.
+The array can be used as soon as it has been created. There is no
+need to wait for the initial resync to finish.
.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
+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.
+of component devices and changing the number of active devices in RAID
+levels 1/4/5/6, changing the RAID level between 1, 5, and 6, changing
+the chunk size and layout for RAID5 and RAID5, 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.
+
+If a
+.B CONTAINER
+is passed to
+.I mdadm
+in this mode, then any arrays within that container will be assembled
+and started.
.TP
.B Manage
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.
+.\"This mode allows operations on independent devices such as examine MD
+.\"superblocks, erasing old superblocks and stopping active arrays.
+.TP
+.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
.SH Options for selecting a mode are:
.TP
-.BR -A ", " --assemble
+.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 -F ", " --follow ", " --monitor
+.BR \-F ", " \-\-follow ", " \-\-monitor
Select
.B Monitor
mode.
.TP
-.BR -G ", " --grow
+.BR \-G ", " \-\-grow
Change the size or shape of an active array.
+
+.TP
+.BR \-I ", " \-\-incremental
+Add a single device into an appropriate array, and possibly start the array.
+
+.TP
+.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 ,
+and all use v0.90 metadata.
+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 ,
+.BR \-\-add ,
+.BR \-\-fail ,
or
-.BR --remove ,
-then the MANAGE mode is assume.
+.BR \-\-remove ,
+then the MANAGE mode is assumed.
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
+.BR \-h ", " \-\-help
Display general help message or, after one of the above options, a
-mode specific help message.
+mode-specific help message.
.TP
-.B --help-options
+.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
+.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
+.B \-\-detail \-\-scan
and
-.BR "--examine --scan" .
+.BR "\-\-examine \-\-scan" .
.TP
-.BR -q ", " --quiet
+.BR \-q ", " \-\-quiet
Avoid printing purely informative messages. With this,
-.B mdadm
+.I mdadm
will be silent unless there is something really important to report.
.TP
-.BR -b ", " --brief
-Be less verbose. This is used with
-.B --detail
-and
-.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=
+.BR \-c ", " \-\-config=
Specify the config file. Default is to use
.BR /etc/mdadm.conf ,
-or if that is missing, then
+or if that is missing then
.BR /etc/mdadm/mdadm.conf .
If the config file given is
-.B partitions
+.B "partitions"
then nothing will be read, but
.I mdadm
will act as though the config file contained exactly
-.B "DEVICE partitions"
+.B "DEVICE partitions containers"
and will read
.B /proc/partitions
-to find a list of devices to scan.
+to find a list of devices to scan, and
+.B /proc/mdstat
+to find a list of containers to examine.
If the word
-.B none
+.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
+.I mdadm
+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 .
.TP
-.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.
+.BR \-e ", " \-\-metadata=
+Declare the style of RAID metadata (superblock) to be used. The
+default is 1.2 for
+.BR \-\-create ,
+and to guess for other operations.
The default can be overridden by setting the
.B metadata
value for the
Options are:
.RS
-.IP "0, 0.90, default"
+.IP "0, 0.90"
Use the original 0.90 format superblock. This format limits arrays to
-28 componenet devices and limits component devices of levels 1 and
+28 component devices and limits component devices of levels 1 and
greater to 2 terabytes.
-.IP "1, 1.0, 1.1, 1.2"
+.IP "1, 1.0, 1.1, 1.2 default"
Use the new version-1 format superblock. This has few restrictions.
-The different subversion store the superblock at different locations
+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).
+4K from the start (for 1.2). '1' is equivalent to '1.0', 'default' is
+equivalent to '1.2'.
+.IP ddf
+Use the "Industry Standard" DDF (Disk Data Format) format defined by
+SNIA.
+When creating a DDF array a
+.B CONTAINER
+will be created, and normal arrays can be created in that container.
+.IP imsm
+Use the Intel(R) Matrix Storage Manager metadata format. This creates a
+.B CONTAINER
+which is managed in a similar manner to DDF, and is supported by an
+option-rom on some platforms:
+.IP
+.B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
+.PP
.RE
.TP
-.B --homehost=
-This will over-ride any
+.B \-\-homehost=
+This will override any
.B HOMEHOST
-setting in the config file and provides the identify of the host which
+setting in the config file and provides the identity of the host which
should be considered the home for any arrays.
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
+will be recorded in the metadata. 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.
for the given homehost will be reported as such.
When using Auto-Assemble, only arrays tagged for the given homehost
-will be assembled.
+will be allowed to use 'local' names (i.e. not ending in '_' followed
+by a digit string). See below under
+.BR "Auto Assembly" .
.SH For create, build, or grow:
.TP
-.BR -n ", " --raid-devices=
+.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 .
+.BR \-\-create .
Setting a value of 1 is probably
a mistake and so requires that
-.B --force
+.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.
+multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
.br
This number can only be changed using
-.B --grow
-for RAID1 arrays, and only on kernels which provide necessary support.
+.B \-\-grow
+for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
+the necessary support.
.TP
-.BR -x ", " --spare-devices=
+.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
+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 RAID1/4/5/6.
+.BR \-z ", " \-\-size=
+Amount (in Kibibytes) of space to use from each drive in RAID levels 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
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
+.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 .
+.BR \-\-grow .
The size can be given as
.B max
which means to choose the largest size that fits on all current drives.
+This value can not be used with
+.B CONTAINER
+metadata such as DDF and IMSM.
+
+.TP
+.BR \-Z ", " \-\-array-size=
+This is only meaningful with
+.B \-\-grow
+and its effect is not persistent: when the array is stopped an
+restarted the default array size will be restored.
+
+Setting the array-size causes the array to appear smaller to programs
+that access the data. This is particularly needed before reshaping an
+array so that it will be smaller. As the reshape is not reversible,
+but setting the size with
+.B \-\-array-size
+is, it is required that the array size is reduced as appropriate
+before the number of devices in the array is reduced.
+
.TP
-.BR -c ", " --chunk=
-Specify chunk size of kibibytes. The default is 64.
+.BR \-c ", " \-\-chunk=
+Specify chunk size of kibibytes. The default when creating an
+array is 512KB. To ensure compatibility with earlier versions, the
+default when Building and array with no persistent metadata is 64KB.
+This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
.TP
-.BR --rounding=
-Specify rounding factor for linear array (==chunk size)
+.BR \-\-rounding=
+Specify rounding factor for a Linear array. The size of each
+component will be rounded down to a multiple of this size.
+This is a synonym for
+.B \-\-chunk
+but highlights the different meaning for Linear as compared to other
+RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
+use, and is 0K (i.e. no rounding) in later kernels.
.TP
-.BR -l ", " --level=
-Set raid level. When used with
-.IR --create ,
+.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.
+raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
+Obviously some of these are synonymous.
+
+When a
+.B CONTAINER
+metadata type is requested, only the
+.B container
+level is permitted, and it does not need to be explicitly given.
When used with
-.IR --build ,
+.BR \-\-build ,
only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
Not yet supported with
-.IR --grow .
+.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
+.BR \-p ", " \-\-layout=
+This option configures the fine details of data layout for RAID5, RAID6,
+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.
+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 .
+
+It is also possibly to cause RAID5 to use a RAID4-like layout by
+choosing
+.BR parity\-first ,
+or
+.BR parity\-last .
-When setting the failure mode for
-.I faulty
+Finally for RAID5 there are DDF\-compatible layouts,
+.BR ddf\-zero\-restart ,
+.BR ddf\-N\-restart ,
+and
+.BR ddf\-N\-continue .
+
+These same layouts are available for RAID6. There are also 4 layouts
+that will provide an intermediate stage for converting between RAID5
+and RAID6. These provide a layout which is identical to the
+corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
+syndrome (the second 'parity' block used by RAID6) on the last device.
+These layouts are:
+.BR left\-symmetric\-6 ,
+.BR right\-symmetric\-6 ,
+.BR left\-asymmetric\-6 ,
+.BR right\-asymmetric\-6 ,
+and
+.BR parity\-first\-6 .
+
+When setting the failure mode for level
+.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
+.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 request, and will continue to be generated
+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
-"--grow" option to set subsequent failure modes.
+.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 "--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:
-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
+.I 'n'
+signals 'near' copies. Multiple copies of one data block are at
similar offsets in different devices.
-.I o
+.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
+.I 'f'
signals 'far' copies
-(multiple copies have very different offsets). See md(4) for more
-detail about 'near' and 'far'.
+(multiple copies have very different offsets).
+See md(4) for more detail about 'near', 'offset', 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
number (e.g. it is perfectly legal to have an 'n2' layout for an array
with an odd number of devices).
+When an array is converted between RAID5 and RAID6 an intermediate
+RAID6 layout is used in which the second parity block (Q) is always on
+the last device. To convert a RAID5 to RAID6 and leave it in this new
+layout (which does not require re-striping) use
+.BR \-\-layout=preserve .
+This will try to avoid any restriping.
+
+The converse of this is
+.B \-\-layout=normalise
+which will change a non-standard RAID6 layout into a more standard
+arrangement.
+
.TP
-.BR --parity=
-same as --layout (thus explaining the p of
-.IR -p ).
+.BR \-\-parity=
+same as
+.B \-\-layout
+(thus explaining the p of
+.BR \-p ).
.TP
-.BR -b ", " --bitmap=
+.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
+exist unless
+.B \-\-force
+is also given. The same file should be provided
when assembling the array. If the word
-.B internal
+.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
+.B "none"
is given with
-.B --grow
+.B \-\-grow
mode, then any bitmap that is present is removed.
To help catch typing errors, the filename must contain at least one
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
+.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.
+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.
-
+bitmap, the chunksize defaults to 64Meg, or larger if necessary to
+fit the bitmap into the available space.
.TP
-.BR -W ", " --write-mostly
-subsequent devices lists in a
-.BR --build ,
-.BR --create ,
+.BR \-W ", " \-\-write\-mostly
+subsequent devices listed in a
+.BR \-\-build ,
+.BR \-\-create ,
or
-.B --add
+.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=
+.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.
+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
+.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.
+initial resync, however this practice \(em while normally safe \(em is not
+recommended. Use this only if you really know what you are doing.
+.IP
+When the devices that will be part of a new array were filled
+with zeros before creation the operator knows the array is
+actually clean. If that is the case, such as after running
+badblocks, this argument can be used to tell mdadm the
+facts the operator knows.
.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.
+.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 GROW MODE section below on RAID\-DEVICES CHANGES. The file
+should be stored on a separate device, not on the RAID array being
+reshaped.
+
+.TP
+.BR \-\-array-size= ", " \-Z
+Set the size of the array which is seen by users of the device such as
+filesystems. This can be less that the real size, but never greater.
+The size set this way does not persist across restarts of the array.
+
+This is most useful when reducing the number of devices in a RAID5 or
+RAID6. Such arrays require the array-size to be reduced before a
+reshape can be performed that reduces the real size.
+
+A value of
+.B max
+restores the apparent size of the array to be whatever the real
+amount of available space is.
.TP
-.BR -N ", " --name=
+.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.
+array with a version-1 superblock, or an array in a DDF container.
+The name is a simple textual string that can be used to identify array
+components when assembling. If name is needed but not specified, it
+is taken from the basename of the device that is being created.
+e.g. when creating
+.I /dev/md/home
+the
+.B name
+will default to
+.IR home .
.TP
-.BR -R ", " --run
+.BR \-R ", " \-\-run
Insist that
.I mdadm
run the array, even if some of the components
array. This option causes that question to be suppressed.
.TP
-.BR -f ", " --force
+.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
+to create a RAID5 array with one missing drive (as this makes the
initial resync work faster). With
-.BR --force ,
+.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
+.BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
+Instruct mdadm how 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
+to be used (though since Linux 2.6.28, these array devices are in fact
+partitionable). "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.
+from this. With mdadm 3.0, device creation is normally left up to
+.I udev
+so this option is unlikely to be needed.
+See DEVICE NAMES below.
The argument can also come immediately after
-"-a". e.g. "-ap".
+"\-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
-.I --scan
+.B \-\-scan
is also given, then any
.I auto=
-entries in the config file will over-ride the
-.I --auto
+entries in the config file will override the
+.B \-\-auto
instruction given on the command line.
For partitionable arrays,
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 ).
+.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".
+and a number, e.g.
+.IR /dev/md/home1p3 .
+If there is no trailing digit, then the partition names just have a
+number added, e.g.
+.IR /dev/md/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
+device number based on that name. If the device name is not in one of these
+formats, then a unused device number will be allocated. The device
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 .
-
+non-standard name. Names that are not in 'standard' format are only
+allowed in "/dev/md/".
+
+.ig XX
+.\".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 .
+.\"
+.XX
.SH For assemble:
.TP
-.BR -u ", " --uuid=
-uuid of array to assemble. Devices which don't have this uuid are
+.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 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
+.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
+.B \-\-super\-minor=dev
will look for super blocks with a minor number of 0.
+.B \-\-super\-minor
+is only relevant for v0.90 metadata, and should not normally be used.
+Using
+.B \-\-uuid
+is much safer.
+
.TP
-.BR -N ", " --name=
+.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
+the name stored in the superblock exactly, or it must match
with the current
.I homehost
-is added to the start of the given name.
+prefixed to the start of the given name.
.TP
-.BR -f ", " --force
-Assemble the array even if some superblocks appear out-of-date
+.BR \-f ", " \-\-force
+Assemble the array even if the metadata on some devices appears to be
+out-of-date. If
+.I mdadm
+cannot find enough working devices to start the array, but can find
+some devices that are recorded as having failed, then it will mark
+those devices as working so that the array can be started.
+An array which requires
+.B \-\-force
+to be started may contain data corruption. Use it carefully.
.TP
-.BR -R ", " --run
+.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
+.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
+.B \-\-no\-degraded
This is the reverse of
-.B --run
-in that it inhibits the started if array unless all expected drives
+.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 you physical connections to devices are
+.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}"
+.BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
See this option under Create and Build options.
.TP
-.BR -b ", " --bitmap=
+.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=
+.BR \-\-backup\-file=
If
-.B --backup-file
+.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.
+.B \-\-backup\-file
+must be presented to
+.B \-\-assemble
+to allow possibly corrupted data to be restored.
.TP
-.BR -U ", " --update=
+.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 byteorder ,
.BR devicesize ,
or
-.BR super-minor .
+.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"
+.B "\-\-examine \-\-sparc2.2"
option to
.I mdadm
to see what effect this would have.
The
-.B super-minor
+.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
+.B \-\-examine
reports a different "Preferred Minor" to
-.BR --detail .
+.BR \-\-detail .
In some cases this update will be performed automatically
-by the kernel driver. In particular the update happens 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 \-\-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.
+If no
+.B \-\-uuid
+is given, a random UUID is chosen.
The
.B name
.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
+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.
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"
+.B "\-\-update=byteorder"
will cause
.I mdadm
to expect superblocks to have their byteorder reversed, and will
The
.B summaries
-option will correct the summaries in the superblock. That is the
+option will correct the summaries in the superblock. That is the
counts of total, working, active, failed, and spare devices.
The
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 .
+.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.
+.ig
.TP
-.B --auto-update-homehost
-This flag is only meaning with auto-assembly (see discussion below).
+.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 recan for any arrays at all and will assemble them and update the
+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
-hot-add listed devices.
+.BR \-a ", " \-\-add
+hot-add listed devices. For arrays with redundancy, the listed
+devices become available as spares. If the array is degraded, it will
+immediately start recovering data on to one of these spares.
.TP
-.BR --re-add
-re-add a device that was recently removed from an array.
+.BR \-\-re\-add
+re-add a device that was recently removed from an array. This is only
+needed for arrays that have be built (i.e. with
+.BR --build ).
+For created arrays, devices are always re-added if that is possible.
+When re-adding a device, if nothing has changed on the array since the
+device was removed, no recovery is performed. Also, if the array has
+a write-intent bitmap, then the recovery performed after a re-add will
+be limited to those blocks which, according to the bitmap, might have
+changed since the device was removed.
.TP
-.BR -r ", " --remove
+.BR \-r ", " \-\-remove
remove listed devices. They must not be active. i.e. they should
-be failed or spare devices.
+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 -f ", " --fail
-mark listed devices as faulty.
+.BR \-\-set\-faulty
+same as
+.BR \-\-fail .
.TP
-.BR --set-faulty
-same as --fail.
+.BR \-\-write\-mostly
+Subsequent devices that are added or re-added will have the 'write-mostly'
+flag set. This is only valid for RAID1 and means that the 'md' driver
+will avoid reading from these devices if possible.
+.TP
+.BR \-\-readwrite
+Subsequent devices that are added or re-added will have the 'write-mostly'
+flag cleared.
.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
+Each of these options requires that the first device listed is the array
+to be acted upon, and the remainder are component devices to be added,
+removed, marked as faulty, etc. 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
+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.
+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 updated the blocks that have changed
+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
+.B \-\-build
mdadm needs to be told that this device we removed recently with
-.B --re-add.
+.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 be marked as
-.B faulty
-first.
+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 -Q ", " --query
+.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.
+.BR \-D ", " \-\-detail
+Print details of one or more md devices.
.TP
-.BR -E ", " --examine
-Print content of md superblock on device(s).
+.BR \-\-detail\-platform
+Print details of the platform's RAID capabilities (firmware / hardware
+topology) for a given metadata format.
+
+.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
-.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
+.BR \-E ", " \-\-examine
+Print contents of the metadata stored on the named device(s).
+Note the contrast between
+.B \-\-examine
+and
+.BR \-\-detail .
+.B \-\-examine
+applies to devices which are components of an array, while
+.B \-\-detail
+applies to a whole array which is currently active.
+.TP
+.B \-\-sparc2.2
+If an array was created on a SPARC machine with 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
+.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" .
+.BR "\-\-assemble \-\-update=sparc2.2" .
.TP
-.BR -X ", " --examine-bitmap
+.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. Note that running this on an array
+device (e.g.
+.BR /dev/md0 )
+does not report the bitmap for that array.
.TP
-.BR -R ", " --run
-start a partially built array.
+.BR \-R ", " \-\-run
+start a partially assembled array. If
+.B \-\-assemble
+did not find enough devices to fully start the array, it might leaving
+it partially assembled. If you wish, you can then use
+.B \-\-run
+to start the array in degraded mode.
.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
+.BR \-t ", " \-\-test
When used with
-.BR --detail ,
+.BR \-\-detail ,
the exit status of
.I mdadm
-is set to reflect the status of the device.
+is set to reflect the status of the device. See below in
+.B MISC MODE
+for details.
+
+.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.
+
+.TP
+.BR \-\-wait\-clean
+For each md device given, or each device in /proc/mdstat if
+.B \-\-scan
+is given, arrange for the array to be marked clean as soon as possible.
+Also, quiesce resync so that the monitor for external metadata arrays
+(mdmon) has an opportunity to checkpoint the resync position.
+.I mdadm
+will return with success if the array uses external metadata and we
+successfully waited. For native arrays this returns immediately as the
+kernel handles both dirty-clean transitions and resync checkpointing in
+the kernel at shutdown. No action is taken if safe-mode handling is
+disabled.
+
+.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
+.B \-\-no\-degraded
+This allows the hot-plug system to prevent arrays from running when it knows
+that more disks may arrive later in the discovery process.
+
+.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 -y ", " --syslog
+.BR \-y ", " \-\-syslog
Cause all events to be reported through 'syslog'. The messages have
facility of 'daemon' and varying priorities.
.TP
-.BR -d ", " --delay
+.BR \-d ", " \-\-delay
Give a delay in seconds.
-.B mdadm
+.I mdadm
polls the md arrays and then waits this many seconds before polling
-again. The default is 60 seconds.
+again. The default is 60 seconds. Since 2.6.16, there is no need to
+reduce this as the kernel alerts
+.I mdadm
+immediately when there is any change.
.TP
-.BR -f ", " --daemonise
+.BR \-r ", " \-\-increment
+Give a percentage increment.
+.I mdadm
+will generate RebuildNN events with the given percentage increment.
+
+.TP
+.BR \-f ", " \-\-daemonise
Tell
-.B mdadm
+.I 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
+causes it to fork and run in the child, and to disconnect from the
terminal. The process id of the child is written to stdout.
This is useful with
-.B --scan
+.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
+.BR \-i ", " \-\-pid\-file
When
-.B mdadm
+.I 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
+.BR \-1 ", " \-\-oneshot
Check arrays only once. This will generate
.B NewArray
events and more significantly
.B SparesMissing
events. Running
.in +5
-.B " mdadm --monitor --scan -1"
+.B " mdadm \-\-monitor \-\-scan \-1"
.in -5
from a cron script will ensure regular notification of any degraded arrays.
.TP
-.BR -t ", " --test
+.BR \-t ", " \-\-test
Generate a
.B TestMessage
alert for every array found at startup. This alert gets mailed and
.HP 12
Usage:
-.B mdadm --assemble
+.B mdadm \-\-assemble
.I md-device options-and-component-devices...
.HP 12
Usage:
-.B mdadm --assemble --scan
-.I md-devices-and-options...
+.B mdadm \-\-assemble \-\-scan
+.I md-devices-and-options...
.HP 12
Usage:
-.B mdadm --assemble --scan
-.I options...
+.B mdadm \-\-assemble \-\-scan
+.I options...
.PP
-This usage assembles one or more raid arrays from pre-existing components.
+This usage assembles one or more RAID arrays from pre-existing components.
For each array, mdadm needs to know the md device, the identity of the
-array, and a number of component-devices. These can be found in a number of ways.
+array, and a number of component-devices. These can be found in a number of ways.
In the first usage example (without the
-.BR --scan )
+.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.
+listed in the configuration file are assembled. If not arrays are
+described by the configuration file, then any arrays that
+can be found on unused devices will be assembled.
If precisely one device is listed, but
-.B --scan
+.B \-\-scan
is not given, then
.I mdadm
acts as though
-.B --scan
-was given and identify information is extracted from the configuration file.
+.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 the config file, or will be taken from the
-super block on the first component-device listed on the command line.
+.B \-\-uuid
+option, the
+.B \-\-name
+option, or the
+.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
+.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
+.B \-\-config
or requested with (a possibly implicit)
-.B --scan.
+.BR \-\-scan .
In the later case,
.B /etc/mdadm.conf
+or
+.B /etc/mdadm/mdadm.conf
is used.
If
-.B --scan
+.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 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, 4, 5, 6, or 10), give the
-.B --run
+.B \-\-scan
+is not given and not all expected drives were listed, 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, 4, 5, 6, or 10),
+give the
+.B \-\-run
flag.
-If an
-.B auto
-option is given, either on the command line (--auto) or in the
-configuration file (e.g. auto=part), then
+If
+.I udev
+is active,
.I mdadm
-will create the md device if necessary or will re-create it if it
-doesn't look usable as it is.
-
-This can be useful for handling partitioned devices (which don't have
-a stable device number - it can change after a reboot) and when using
-"udev" to manage your
+does not create any entries in
.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.
+but leaves that to
+.IR udev .
+It does record information in
+.B /var/run/mdadm/map
+which will allow
+.I udev
+to choose the correct name.
-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.
+If
+.I mdadm
+detects that udev is not configured, it will create the devices in
+.B /dev
+itself.
-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.
+In Linux kernels prior to version 2.6.28 there were two distinctly
+different types of md devices that could be created: one that could be
+partitioned using standard partitioning tools and one that could not.
+Since 2.6.28 that distinction is no longer relevant as both type of
+devices can be partitioned.
+.I mdadm
+will normally create the type that originally could not be partitioned
+as it has a well defined major number (9).
+
+Prior to 2.6.28, it is important that mdadm chooses the correct type
+of array device to use. This can be controlled with the
+.B \-\-auto
+option. In particular, a value of "mdp" or "part" or "p" tells mdadm
+to use a partitionable device rather than the default.
+
+In the no-udev case, the value given to
+.B \-\-auto
+can be suffixed by a number. This tells
+.I mdadm
+to create that number of partition devices rather than the default of 4.
-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.
+The value given to
+.B \-\-auto
+can also be given in the configuration file as a word starting
+.B auto=
+on the ARRAY line for the relevant array.
.SS Auto Assembly
When
-.B --assemble
+.B \-\-assemble
is used with
-.B --scan
+.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.
+In no array at listed in the config (other than those marked
+.BR <ignore> )
+it will look through the available devices for possible arrays and
+will try to assemble anything that it finds. Arrays which are tagged
+as belonging to the given homehost will be assembled and started
+normally. Arrays which do not obviously belong to this host are given
+names that are expected not to conflict with anything local, and are
+started "read-auto" so that nothing is written to any device until the
+array is written to. i.e. automatic resync etc is delayed.
If
.I mdadm
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.
-
+.B /dev/md/
+(the name will have any 'host' prefix stripped first).
+
+This behaviour can be modified by the
+.I AUTO
+line in the
+.I mdadm.conf
+configuration file. This line can indicate that specific metadata
+type should, or should not, be automatically assembled. If an array
+is found which is not listed in
+.I mdadm.conf
+and has a metadata format that is denied by the
+.I AUTO
+line, then it will not be assembled.
+The
+.I AUTO
+line can also request that all arrays identified as being for this
+homehost should be assembled regardless of their metadata type.
+See
+.IR mdadm.conf (5)
+for further details.
+
+.ig
If
.I mdadm
cannot find any array for the given host at all, and if
-.B --auto-update-homehost
+.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 .
+.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
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-devices= 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 an array without a superblock. With
+.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 raid0, linear, multipath, or faulty, or one of their
-synonyms. All devices must be listed and the array will be started
-once complete.
+The level may raid0, linear, raid1, raid10, multipath, or faulty, or
+one of their synonyms. All devices must be listed and the array will
+be started once complete. It will often be appropriate to use
+.B \-\-assume\-clean
+with levels raid1 or raid10.
.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-devices= Z
-.I devices
+.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.
+The named device will normally not exist when
+.I "mdadm \-\-create"
+is run, but will be created by
+.I udev
+once the array becomes active.
-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
+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
-.B --run
+.B \-\-run
can override this caution.
To create a "degraded" array in which some devices are missing, simply
give the word "\fBmissing\fP"
in place of a device name. This will cause
-.B mdadm
+.I 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.
"\fBmissing\fP".
When creating a RAID5 array,
-.B mdadm
+.I 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
+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
+When creating an array with version-1 metadata a name for the array is
required.
If this is not given with the
-.B --name
+.B \-\-name
option,
.I mdadm
-will chose a name based on the last component of the name of the
+will choose 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 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 --size
-'''is given, the apparent size of the smallest drive given is used.
+When creating a partition based array, using
+.I mdadm
+with version-1.x metadata, the partition type should be set to
+.B 0xDA
+(non fs-data). This type selection allows for greater precision since
+using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
+might create problems in the event of array recovery through a live cdrom.
+
+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.
+
+When creating an array within a
+.B CONTAINER
+.I mdadm
+can be given either the list of devices to use, or simply the name of
+the container. The former case gives control over which devices in
+the container will be used for the array. The latter case allows
+.I mdadm
+to automatically choose which devices to use based on how much spare
+space is available.
-The General Management options that are valid with --create are:
+The General Management options that are valid with
+.B \-\-create
+are:
.TP
-.B --run
+.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
This usage will allow individual devices in an array to be failed,
removed or added. It is possible to perform multiple operations with
-on command. For example:
+on command. For example:
.br
-.B " 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
in as a spare. However only one md array can be affected by a single
command.
+When a device is added to an active array, mdadm checks to see if it
+has metadata on it which suggests that it was recently a member of the
+array. If it does, it tried to "re-add" the device. If there have
+been no changes since the device was removed, or if the array has a
+write-intent bitmap which has recorded whatever changes there were,
+then the device will immediately become a full member of the array and
+those differences recorded in the bitmap will be resolved.
+
.SH MISC MODE
.HP 12
Usage:
.B mdadm
.I options ...
-.I devices ...
+.I devices ...
.PP
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
+.B \-\-detail
The device should be an active md device.
-.B mdadm
+.B mdadm
will display a detailed description of the array.
-.B --brief
+.B \-\-brief
or
-.B --scan
+.B \-\-scan
will cause the output to be less detailed and the format to be
suitable for inclusion in
.BR /etc/mdadm.conf .
.I mdadm
will normally be 0 unless
.I mdadm
-failed to get useful information about the device(s). However if the
-.B --test
+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
The array has at least one failed device.
.TP
2
-The array has multiple failed devices and hence is unusable (raid4 or
-raid5).
+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
+.B \-\-detail\-platform
+Print detail of the platform's RAID capabilities (firmware / hardware
+topology). If the metadata is specified with
+.B \-e
+or
+.B \-\-metadata=
+then the return status will be:
+.RS
+.TP
+0
+metadata successfully enumerated its platform components on this system
+.TP
+1
+metadata is platform independent
+.TP
+2
+metadata failed to find its platform components on this system
+.RE
+
+.TP
+.B \-\-examine
The device should be a component of an md array.
-.B mdadm
+.I 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 .
Having
-.B --scan
+.B \-\-scan
without listing any devices will cause all devices listed in the
config file to be examined.
.TP
---stop
+.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
---scan
+.B \-\-scan
For all operations except
-.BR --examine ,
-.B --scan
+.BR \-\-examine ,
+.B \-\-scan
will cause the operation to be applied to all arrays listed in
.BR /proc/mdstat .
For
-.BR --examine,
-.B --scan
+.BR \-\-examine,
+.B \-\-scan
causes all devices listed in the config file to be examined.
+.TP
+.BR \-b ", " \-\-brief
+Be less verbose. This is used with
+.B \-\-detail
+and
+.BR \-\-examine .
+Using
+.B \-\-brief
+with
+.B \-\-verbose
+gives an intermediate level of verbosity.
.SH MONITOR MODE
.HP 12
Usage:
-.B mdadm --monitor
+.B mdadm \-\-monitor
.I options... devices...
.PP
This usage causes
-.B mdadm
+.I mdadm
to periodically poll a number of md arrays and to report on any events
noticed.
-.B mdadm
+.I mdadm
will never exit once it decides that there are arrays to be checked,
so it should normally be run in the background.
As well as reporting events,
-.B mdadm
+.I 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
+.I 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.
These events are passed to a separate program (if specified) and may
be mailed to a given E-mail address.
-When passing event to program, the program is run once for each event
-and is given 2 or 3 command-line arguments. The first is the
-name of the event (see below). The second is the name of the
+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.
+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
+.I mdadm
will not monitor anything.
Without
-.B --scan
-.B mdadm
+.B \-\-scan,
+.I mdadm
will continue monitoring as long as something was found to monitor. If
no program or email is given, then each event is reported to
.BR stdout .
.BI Rebuild NN
Where
.I NN
-is 20, 40, 60, or 80, this indicates that rebuild has passed that many
-percentage of the total. (syslog priority: Warning)
+is a two-digit number (ie. 05, 48). This indicates that rebuild
+has passed that many percent of the total. The events are generated
+with fixed increment since 0. Increment size may be specified with
+a commandline option (default is 20). (syslog priority: Warning)
.TP
.B RebuildFinished
.TP
.B FailSpare
A spare component device which was being rebuilt to replace a faulty
-device has failed. (syslog priority: Critial)
+device has failed. (syslog priority: Critical)
.TP
.B SpareActive
.B NewArray
A new md array has been detected in the
.B /proc/mdstat
-file. (syslog priority: Info)
+file. (syslog priority: Info)
.TP
.B DegradedArray
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)
+(syslog priority: Critical)
.TP
.B MoveSpare
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
+detects that it has fewer than this number when it first sees the
array, it will report a
.B SparesMissing
message.
.TP
.B TestMessage
An array was found at startup, and the
-.B --test
+.B \-\-test
flag was given.
(syslog priority: Info)
.RE
Only
-.B Fail ,
-.B FailSpare ,
-.B DegradedArray ,
-.B SparesMissing ,
+.B Fail,
+.B FailSpare,
+.B DegradedArray,
+.B SparesMissing
and
.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.
the second device is the array that the spare was moved from.
For
-.B mdadm
+.I 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
+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
+.I mdadm
+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
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.
+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.
+increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
+and RAID6.
+.IP \bu 4
+change the chunk-size and layout of RAID5 and RAID6.
+.IP \bu 4
+convert between RAID1 and RAID5, and between RAID5 and RAID6.
.IP \(bu 4
-add a write-intent bitmap to any array which support these bitmaps, or
+add a write-intent bitmap to any array which supports these bitmaps, or
remove a write-intent bitmap from such an array.
.PP
+GROW mode is not currently supported for
+.B CONTAINERS
+or arrays inside containers.
+
.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
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
+Also the size of an array cannot be changed while it has an active
+bitmap. If an array has a bitmap, it must be removed before the size
+can be changed. Once the change it complete a new bitmap can be created.
+
+.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
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.
+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
+Changing the number of active devices in a RAID5 or RAID6 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".
+back to a new location. From 2.6.17, the Linux Kernel is able to
+increase the number of devices in a RAID5 safely, including restarting
+an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
+increase or decrease the number of devices in a RAID5 or RAID6.
+
+When decreasing the number of devices, the size of the array will also
+decrease. If there was data in the array, it could get destroyed and
+this is not reversible. To help prevent accidents,
+.I mdadm
+requires that the size of the array be decreased first with
+.BR "mdadm --grow --array-size" .
+This is a reversible change which simply makes the end of the array
+inaccessible. The integrity of any data can then be checked before
+the non-reversible reduction in the number of devices is request.
-When relocating the first few stripes on a raid5, it is not possible
+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
+.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
+.B \-\-assemble
to restore the backup and reassemble the array.
+.SS LEVEL CHANGES
+
+Changing the RAID level of any array happens instantaneously. However
+in the RAID to RAID6 case this requires a non-standard layout of the
+RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
+required before the change can be accomplish. So while the level
+change is instant, the accompanying layout change can take quite a
+long time.
+
+.SS CHUNK-SIZE AND LAYOUT CHANGES
+
+Changing the chunk-size of layout without also changing the number of
+devices as the same time will involve re-writing all blocks in-place.
+To ensure against data loss in the case of a crash, a
+.B --backup-file
+must be provided for these changes. Small sections of the array will
+be copied to the backup file while they are being rearranged.
+
+If the reshape is interrupted for any reason, this backup file must be
+make available to
+.B "mdadm --assemble"
+so the array can be reassembled. Consequently the file cannot be
+stored on the device being reshaped.
+
+
.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
+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
+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.
+
+If the device passed is a
+.B CONTAINER
+device created by a previous call to
+.IR mdadm ,
+then rather than trying to add that device to an array, all the arrays
+described by the metadata of the container will be started.
+
+.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.
+
+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.
+
+.ig
+.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.
+..
+
+.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. Or maybe even
+.BR /dev/.mdadm.map ).
+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.
+
+If the array is not found in the config file and its metadata does not
+identify it as belonging to the "homehost", then
+.I mdadm
+will choose a name for the array which is certain not to conflict with
+any array which does belong to this host. It does this be adding an
+underscore and a small number to the name preferred by the metadata.
+
+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
+.I 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 ENVIRONMENT
+This section describes environment variables that affect how mdadm
+operates.
+
+.TP
+.B MDADM_NO_MDMON
+Setting this value to 1 will prevent mdadm from automatically launching
+mdmon. This variable is intended primarily for debugging mdadm/mdmon.
+
+.TP
+.B MDADM_NO_UDEV
+Normally,
+.I mdadm
+does not create any device nodes in /dev, but leaves that task to
+.IR udev .
+If
+.I udev
+appears not to be configured, or if this environment variable is set
+to '1', the
+.I mdadm
+will create and devices that are needed.
+
.SH EXAMPLES
-.B " mdadm --query /dev/name-of-device"
+.B " mdadm \-\-query /dev/name-of-device"
.br
-This will find out if a given device is a raid array, or is part of
+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"
+.B " mdadm \-\-assemble \-\-scan"
.br
-This will assemble and start all arrays listed in the standard config file
+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"
+.B " mdadm \-\-stop \-\-scan"
.br
-This will shut down all array that can be shut down (i.e. are not
+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"
+.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"
+.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"
+.B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
.br
-.B " mdadm --detail --scan >> mdadm.conf"
+.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"
+.B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
+.br
+.B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
.br
-.B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
-.ber
-This will find what arrays could be assembled from existing IDE and
-SCSI whole drives (not partitions) and store the information is the
+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
entries. It should be reviewed and edited before being used as an
actual config file.
-.B " mdadm --examine --brief --scan --config=partitions"
+.B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
.br
-.B " mdadm -Ebsc partitions"
+.B " mdadm \-Ebsc partitions"
.br
Create a list of devices by reading
.BR /proc/partitions ,
scan these for RAID superblocks, and printout a brief listing of all
-that was found.
+that were found.
-.B " mdadm -Ac partitions -m 0 /dev/md0"
+.B " mdadm \-Ac partitions \-m 0 /dev/md0"
.br
Scan all partitions and devices listed in
.BR /proc/partitions
.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"
+.B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
.br
If config file contains a mail address or alert program, run mdadm in
the background in monitor mode monitoring all md devices. Also write
pid of mdadm daemon to
.BR /var/run/mdadm .
-.B " mdadm --create --help"
+.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 --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
+.br
+The array
+.B /dev/md4
+which is currently a RAID5 array will be converted to RAID6. There
+should normally already be a spare drive attached to the array as a
+RAID6 needs one more drive than a matching RAID5.
+
+.B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
+.br
+Create a DDF array over 6 devices.
+
+.B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
+.br
+Create a RAID5 array over any 3 devices in the given DDF set. Use
+only 30 gigabytes of each device.
+
+.B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
+.br
+Assemble a pre-exist ddf array.
+
+.B " mdadm -I /dev/md/ddf1"
+.br
+Assemble all arrays contained in the ddf array, assigning names as
+appropriate.
+
+.B " mdadm \-\-create \-\-help"
.br
Provide help about the Create mode.
-.B " mdadm --config --help"
+.B " mdadm \-\-config \-\-help"
.br
Provide help about the format of the config file.
-.B " mdadm --help"
+.B " mdadm \-\-help"
.br
Provide general help.
-
.SH FILES
.SS /proc/mdstat
filesystem,
.B /proc/mdstat
lists all active md devices with information about them.
-.B mdadm
+.I mdadm
uses this to find arrays when
-.B --scan
+.B \-\-scan
is given in Misc mode, and to monitor array reconstruction
on Monitor mode.
-
.SS /etc/mdadm.conf
The config file lists which devices may be scanned to see if
.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. If
+.B /var/run
+is not available (as may be the case during early boot),
+.B /dev/.mdadm.map
+is used on the basis that
+.B /dev
+is usually available very early in boot.
+
.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.
+understand two sorts of names for array devices.
+
+The first is the so-called 'standard' format name, which matches the
+names used by the kernel and which appear in
+.IR /proc/mdstat .
+
+The second sort can be freely chosen, but must reside in
+.IR /dev/md/ .
+When giving a device name to
+.I mdadm
+to create or assemble an array, either full path name such as
+.I /dev/md0
+or
+.I /dev/md/home
+can be given, or just the suffix of the second sort of name, such as
+.I home
+can be given.
+
+When
+.I mdadm
+chooses device names during auto-assembly or incremental assembly, it
+will sometimes add a small sequence number to the end of the name to
+avoid conflicted between multiple arrays that have the same name. If
+.I mdadm
+can reasonably determine that the array really is meant for this host,
+either by a hostname in the metadata, or by the presence of the array
+in /etc/mdadm.conf, then it will leave off the suffix if possible.
+Also if the homehost is specified as
+.B <ignore>
+.I mdadm
+will only use a suffix if a different array of the same name already
+exists or is listed in the config file.
The standard names for non-partitioned arrays (the only sort of md
-array available in 2.4 and earlier) either of
+array available in 2.4 and earlier) are of the form
.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
+onwards) are of the form
.IP
-/dev/md/dNN
-.br
/dev/md_dNN
.PP
Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
+.PP
+From kernel version, 2.6.28 the "non-partitioned array" can actually
+be partitioned. So the "md_dNN" names are no longer needed, and
+partitions such as "/dev/mdNNpXX" are possible.
.SH NOTE
-.B mdadm
+.I mdadm
was previously known as
-.BR mdctl .
+.IR mdctl .
.P
-.B mdadm
+.I mdadm
is completely separate from the
-.B raidtools
+.I 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 mdadm usage, MD and the various levels of
+RAID, see:
.IP
-.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
+.B http://linux\-raid.osdl.org/
+.PP
+(based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
+.\".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
The latest version of
.I mdadm
should always be available from
.IP
-.UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
-http://www.kernel.org/pub/linux/utils/raid/mdadm/
-.UE
+.B http://www.kernel.org/pub/linux/utils/raid/mdadm/
+.PP
+Related man pages:
.PP
+.IR mdmon (8),
.IR mdadm.conf (5),
.IR md (4).
.PP
projects / thirdparty / mdadm.git / blobdiff