.\" -*- nroff -*-
-.TH MDADM 8 "" v1.10.0
+''' Copyright Neil Brown and others.
+''' This program is free software; you can redistribute it and/or modify
+''' it under the terms of the GNU General Public License as published by
+''' the Free Software Foundation; either version 2 of the License, or
+''' (at your option) any later version.
+''' See file COPYING in distribution for details.
+.TH MDADM 8 "" v2.5.6
.SH NAME
mdadm \- manage MD devices
.I aka
.BI mdadm " [mode] <raiddevice> [options] <component-devices>"
-.SH DESCRIPTION
+.SH DESCRIPTION
RAID devices are virtual devices created from two or more
real block devices. This allows multiple devices (typically disk
drives or partitions there-of) to be combined into a single device to
.BR RAID4 ,
.BR RAID5 ,
.BR RAID6 ,
+.BR RAID10 ,
.BR MULTIPATH ,
and
.BR FAULTY .
-.B MULTIPATH is not a Software RAID mechanism, but does involve
+.B MULTIPATH
+is not a Software RAID mechanism, but does involve
multiple devices. For
.B MULTIPATH
each device is a path to one common physical storage device.
-.B FAULTY is also no true RAID, and it only involves one device. It
+.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 an different purpose.
+'''.B mdadm
+'''is a program that can be used to create, manage, and monitor
+'''MD devices. As
+'''such it provides a similar set of functionality to the
+'''.B raidtools
+'''packages.
+'''The key differences between
+'''.B mdadm
+'''and
+'''.B raidtools
+'''are:
+'''.IP \(bu 4
+'''.B mdadm
+'''is a single program and not a collection of programs.
+'''.IP \(bu 4
+'''.B mdadm
+'''can perform (almost) all of its functions without having a
+'''configuration file and does not use one by default. Also
+'''.B mdadm
+'''helps with management of the configuration
+'''file.
+'''.IP \(bu 4
+'''.B mdadm
+'''can provide information about your arrays (through Query, Detail, and Examine)
+'''that
+'''.B raidtools
+'''cannot.
+'''.P
+'''.I mdadm
+'''does not use
+'''.IR /etc/raidtab ,
+'''the
+'''.B raidtools
+'''configuration file, at all. It has a different configuration file
+'''with a different format and a different purpose.
.SH MODES
mdadm has 7 major modes of operation:
.B Assemble
Assemble the parts of a previously created
array into an active array. Components can be explicitly given
-or can be searched for.
+or can be searched for.
.B mdadm
checks that the components
do form a bona fide array, and can, on request, fiddle superblock
.TP
.B Build
-Build a legacy array without per-device superblocks.
+Build an array that doesn't have per-device superblocks. For these
+sorts of arrays,
+.I mdadm
+cannot differentiate between initial creation and subsequent assembly
+of an array. It also cannot perform any checks that appropriate
+devices have been requested. Because of this, the
+.B Build
+mode should only be used together with a complete understanding of
+what you are doing.
.TP
.B Create
'''It can progress
'''in several step create-add-add-run or it can all happen with one command.
-.TP
-.B Manage
-This is for doing things to specific components of an array such as
-adding new spares and removing faulty devices.
-
-.TP
-.B Misc
-This mode allows operations on independent devices such as examine MD
-superblocks, erasing old superblocks and stopping active arrays.
-
.TP
.B "Follow or Monitor"
Monitor one or more md devices and act on any state changes. This is
-only meaningful for raid1, 4, 5, 6 or multipath arrays as
+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.
.B "Grow"
Grow (or shrink) an array, or otherwise reshape it in some way.
Currently supported growth options including changing the active size
-of componenet devices in RAID level 1/4/5/6 and changing the number of
+of component devices in RAID level 1/4/5/6 and changing the number of
active devices in RAID1.
+.TP
+.B Manage
+This is for doing things to specific components of an array such as
+adding new spares and removing faulty devices.
+
+.TP
+.B Misc
+This is an 'everything else' mode that supports operations on active
+arrays, operations on component devices such as erasing old superblocks, and
+information gathering operations.
+'''This mode allows operations on independent devices such as examine MD
+'''superblocks, erasing old superblocks and stopping active arrays.
+
.SH OPTIONS
-Available options are:
+.SH Options for selecting a mode are:
.TP
.BR -A ", " --assemble
.BR -C ", " --create
Create a new array.
-.TP
-.BR -Q ", " --query
-Examine a device to see
-(1) if it is an md device and (2) if it is a component of an md
-array.
-Information about what is discovered is presented.
-
-.TP
-.BR -D ", " --detail
-Print detail of one or more md devices.
-
-.TP
-.BR -E ", " --examine
-Print content of md superblock on device(s).
-
.TP
.BR -F ", " --follow ", " --monitor
Select
.TP
.BR -G ", " --grow
Change the size or shape of an active array.
+.P
+If a device is given before any options, or if the first option is
+.BR --add ,
+.BR --fail ,
+or
+.BR --remove ,
+then the MANAGE mode is assume.
+Anything other than these will cause the
+.B Misc
+mode to be assumed.
+
+.SH Options that are not mode-specific are:
.TP
.BR -h ", " --help
-Display help message or, after above option, mode specific help
-message.
+Display general help message or, after one of the above options, a
+mode specific help message.
.TP
.B --help-options
.TP
.BR -v ", " --verbose
-Be more verbose about what is happening.
+Be more verbose about what is happening. This can be used twice to be
+extra-verbose.
+The extra verbosity currently only affects
+.B --detail --scan
+and
+.BR "--examine --scan" .
+
+.TP
+.BR -q ", " --quiet
+Avoid printing purely informative messages. With this,
+.B mdadm
+will be silent unless there is something really important to report.
.TP
.BR -b ", " --brief
.B --detail
and
.BR --examine .
+Using
+.B --brief
+with
+.B --verbose
+gives an intermediate level of verbosity.
.TP
.BR -f ", " --force
.TP
.BR -c ", " --config=
-Specify the config file. Default is
-.BR /etc/mdadm.conf .
+Specify the config file. Default is to use
+.BR /etc/mdadm.conf ,
+or if that is missing, then
+.BR /etc/mdadm/mdadm.conf .
If the config file given is
.B partitions
then nothing will be read, but
says to get a list of array devices from
.BR /proc/mdstat .
-.SH For create or build:
+.TP
+.B -e ", " --metadata=
+Declare the style of superblock (raid metadata) to be used. The
+default is 0.90 for --create, and to guess for other operations.
+The default can be overridden by setting the
+.B metadata
+value for the
+.B CREATE
+keyword in
+.BR mdadm.conf .
+
+Options are:
+.RS
+.IP "0, 0.90, default"
+Use the original 0.90 format superblock. This format limits arrays to
+28 componenet devices and limits component devices of levels 1 and
+greater to 2 terabytes.
+.IP "1, 1.0, 1.1, 1.2"
+Use the new version-1 format superblock. This has few restrictions.
+The different subversion store the superblock at different locations
+on the device, either at the end (for 1.0), at the start (for 1.1) or
+4K from the start (for 1.2).
+.RE
+
+.TP
+.B --homehost=
+This will over-ride any
+.B HOMEHOST
+setting in the config file and provides the identify of the host which
+should be considered the home for any arrays.
+
+When creating an array, the
+.B homehost
+will be recorded in the superblock. For version-1 superblocks, it will
+be prefixed to the array name. For version-0.90 superblocks part of
+the SHA1 hash of the hostname will be stored in the later half of the
+UUID.
+
+When reporting information about an array, any array which is tagged
+for the given homehost will be reported as such.
+
+When using Auto-Assemble, only arrays tagged for the given homehost
+will be assembled.
+
+.SH For create, build, or grow:
+
+.TP
+.BR -n ", " --raid-devices=
+Specify the number of active devices in the array. This, plus the
+number of spare devices (see below) must equal the number of
+.I component-devices
+(including "\fBmissing\fP" devices)
+that are listed on the command line for
+.BR --create .
+Setting a value of 1 is probably
+a mistake and so requires that
+.B --force
+be specified first. A value of 1 will then be allowed for linear,
+multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
+.br
+This number can only be changed using
+.B --grow
+for RAID1 arrays, and only on kernels which provide necessary support.
+
+.TP
+.BR -x ", " --spare-devices=
+Specify the number of spare (eXtra) devices in the initial array.
+Spares can also be added
+and removed later. The number of component devices listed
+on the command line must equal the number of raid devices plus the
+number of spare devices.
+
+
+.TP
+.BR -z ", " --size=
+Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
+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
+(as it normally is not) the smallest drive (or partition) sets the
+size, though if there is a variance among the drives of greater than 1%, a warning is
+issued.
+
+This value can be set with
+.B --grow
+for RAID level 1/4/5/6. If the array was created with a size smaller
+than the currently active drives, the extra space can be accessed
+using
+.BR --grow .
+The size can be given as
+.B max
+which means to choose the largest size that fits on all current drives.
.TP
.BR -c ", " --chunk=
Set raid level. When used with
.IR --create ,
options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
-raid5, 5, raid6, 6, multipath, mp, fautly. Obviously some of these are synonymous.
+raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty. Obviously some of these are synonymous.
When used with
.IR --build ,
-only linear, raid0, 0, stripe are valid.
+only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
+
+Not yet supported with
+.IR --grow .
.TP
-.BR -p ", " --parity=
-Set raid5 parity algorithm. Options are:
+.BR -p ", " --layout=
+This option configures the fine details of data layout for raid5,
+and raid10 arrays, and controls the failure modes for
+.IR faulty .
+
+The layout of the raid5 parity block can be one of
left-asymmetric,
left-symmetric,
right-asymmetric,
right-symmetric,
la, ra, ls, rs. The default is left-symmetric.
-This option is also used to set the failure mode for
-.IR faulty .
-The options are:
+When setting the failure mode for
+.I faulty
+the options are:
write-transient,
wt,
read-transient,
rt,
-write-presistent,
+write-persistent,
wp,
read-persistent,
rp,
"--grow" option to set subsequent failure modes.
"clear" or "none" will remove any pending or periodic failure modes,
-and "flush" will clear any persistant faults.
+and "flush" will clear any persistent faults.
To set the parity with "--grow", the level of the array ("faulty")
must be specified before the fault mode is specified.
+Finally, the layout options for RAID10 are one of 'n', 'o' or 'p' followed
+by a small number. The default is 'n2'.
+
+.I n
+signals 'near' copies. Multiple copies of one data block are at
+similar offsets in different devices.
+
+.I o
+signals 'offset' copies. Rather than the chunks being duplicated
+within a stripe, whole stripes are duplicated but are rotated by one
+device so duplicate blocks are on different devices. Thus subsequent
+copies of a block are in the next drive, and are one chunk further
+down.
+
+.I f
+signals 'far' copies
+(multiple copies have very different offsets). See md(4) for more
+detail about 'near' and 'far'.
+
+The number is the number of copies of each datablock. 2 is normal, 3
+can be useful. This number can be at most equal to the number of
+devices in the array. It does not need to divide evenly into that
+number (e.g. it is perfectly legal to have an 'n2' layout for an array
+with an odd number of devices).
+
.TP
-.BR --layout=
-same as --parity
+.BR --parity=
+same as --layout (thus explaining the p of
+.IR -p ).
.TP
-.BR -n ", " --raid-devices=
-Specify the number of active devices in the array. This, plus the
-number of spare devices (see below) must equal the number of
-.I component-devices
-(including "\fBmissing\fP" devices)
-that are listed on the command line for
-.BR --create .
-Setting a value of 1 is probably
-a mistake and so requires that
-.B --force
-be specified first. A value of 1 will then be allowed for linear,
-multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
-.br
-This number can only be changed using
+.BR -b ", " --bitmap=
+Specify a file to store a write-intent bitmap in. The file should not
+exist unless --force is also given. The same file should be provided
+when assembling the array. If the word
+.B internal
+is given, then the bitmap is stored with the metadata on the array,
+and so is replicated on all devices. If the word
+.B none
+is given with
.B --grow
-for RAID1 arrays, and only on kernels which provide necessary support.
+mode, then any bitmap that is present is removed.
+
+To help catch typing errors, the filename must contain at least one
+slash ('/') if it is a real file (not 'internal' or 'none').
+
+Note: external bitmaps are only known to work on ext2 and ext3.
+Storing bitmap files on other filesystems may result in serious problems.
.TP
-.BR -x ", " --spare-devices=
-Specify the number of spare (eXtra) devices in the initial array.
-Spares can also be added
-and removed later. The number of component devices listed
-on the command line must equal the number of raid devices plus the
-number of spare devices.
+.BR --bitmap-chunk=
+Set the chunksize of the bitmap. Each bit corresponds to that many
+Kilobytes of storage.
+When using a file based bitmap, the default is to use the smallest
+size that is atleast 4 and requires no more than 2^21 chunks.
+When using an
+.B internal
+bitmap, the chunksize is automatically determined to make best use of
+available space.
.TP
-.BR -z ", " --size=
-Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
-This must be a multiple of the chunk size, and must leave about 128Kb
-of space at the end of the drive for the RAID superblock.
-If this is not specified
-(as it normally is not) the smallest drive (or partition) sets the
-size, though if there is a variance among the drives of greater than 1%, a warning is
-issued.
+.BR -W ", " --write-mostly
+subsequent devices lists in a
+.BR --build ,
+.BR --create ,
+or
+.B --add
+command will be flagged as 'write-mostly'. This is valid for RAID1
+only and means that the 'md' driver will avoid reading from these
+devices if at all possible. This can be useful if mirroring over a
+slow link.
-This value can be set with
-.B --grow
-for RAID level 1/4/5/6. If the array was created with a size smaller
-than the currently active drives, the extra space can be accessed
-using
-.BR --grow .
+.TP
+.BR --write-behind=
+Specify that write-behind mode should be enabled (valid for RAID1
+only). If an argument is specified, it will set the maximum number
+of outstanding writes allowed. The default value is 256.
+A write-intent bitmap is required in order to use write-behind
+mode, and write-behind is only attempted on drives marked as
+.IR write-mostly .
.TP
.BR --assume-clean
Tell
.I mdadm
-that the array pre-existed and is known to be clean. This is only
-really useful for Building RAID1 array. Only use this if you really
-know what you are doing. This is currently only supported for --build.
+that the array pre-existed and is known to be clean. It can be useful
+when trying to recover from a major failure as you can be sure that no
+data will be affected unless you actually write to the array. It can
+also be used when creating a RAID1 or RAID10 if you want to avoid the
+initial resync, however this practice - while normally safe - is not
+recommended. Use this ony if you really know what you are doing.
+
+.TP
+.BR --backup-file=
+This is needed when --grow is used to increase the number of
+raid-devices in a RAID5 if there are no spare devices available.
+See the section below on RAID_DEVICE CHANGES. The file should be
+stored on a separate device, not on the raid array being reshaped.
+
+.TP
+.BR -N ", " --name=
+Set a
+.B name
+for the array. This is currently only effective when creating an
+array with a version-1 superblock. The name is a simple textual
+string that can be used to identify array components when assembling.
.TP
.BR -R ", " --run
Instruct mdadm to create the device file if needed, possibly allocating
an unused minor number. "md" causes a non-partitionable array
to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
-later) to be used. "yes" requires the named md device to have a
-'standard' format, and the type and minor number will be determined
+later) to be used. "yes" requires the named md device to have
+a 'standard' format, and the type and minor number will be determined
from this. See DEVICE NAMES below.
-The argumentment can also come immediately after
+The argument can also come immediately after
"-a". e.g. "-ap".
+If --auto is not given on the command line or in the config file, then
+the default will be
+.BR --auto=yes .
+
+If
+.I --scan
+is also given, then any
+.I auto=
+entries in the config file will over-ride the
+.I --auto
+instruction given on the command line.
+
For partitionable arrays,
.I mdadm
will create the device file for the whole array and for the first 4
partitions. A different number of partitions can be specified at the
end of this option (e.g.
.BR --auto=p7 ).
-If the device name ends with a digit, the partition names add a'p',
+If the device name ends with a digit, the partition names add a 'p',
and a number, e.g. "/dev/home1p3". If there is no
trailing digit, then the partition names just have a number added,
e.g. "/dev/scratch3".
If the md device name is in a 'standard' format as described in DEVICE
NAMES, then it will be created, if necessary, with the appropriate
number based on that name. If the device name is not in one of these
-formats, then a unused minor number will be allocted. The minor
+formats, then a unused minor number will be allocated. The minor
number will be considered unused if there is no active array for that
number, and there is no entry in /dev for that number and with a
non-standard name.
+.TP
+.BR --symlink = no
+Normally when
+.B --auto
+causes
+.I mdadm
+to create devices in
+.B /dev/md/
+it will also create symlinks from
+.B /dev/
+with names starting with
+.B md
+or
+.BR md_ .
+Use
+.B --symlink=no
+to suppress this, or
+.B --symlink=yes
+to enforce this even if it is suppressing
+.IR mdadm.conf .
+
+
.SH For assemble:
.TP
.M --super-minor=dev
will look for super blocks with a minor number of 0.
+.TP
+.BR -N ", " --name=
+Specify the name of the array to assemble. This must be the name
+that was specified when creating the array. It must either match
+then name stored in the superblock exactly, or it must match
+with the current
+.I homehost
+is added to the start of the given name.
+
.TP
.BR -f ", " --force
Assemble the array even if some superblocks appear out-of-date
.TP
.BR -R ", " --run
-Attempt to start the array even if fewer drives were given than are
-needed for a full array. Normally if not all drives are found and
+Attempt to start the array even if fewer drives were given than were
+present last time the array was active. Normally if not all the
+expected drives are found and
.B --scan
is not used, then the array will be assembled but not started.
With
.B --run
an attempt will be made to start it anyway.
+.TP
+.B --no-degraded
+This is the reverse of
+.B --run
+in that it inhibits the started if array unless all expected drives
+are present. This is only needed with
+.B --scan
+and can be used if you physical connections to devices are
+not as reliable as you would like.
+
.TP
.BR -a ", " "--auto{=no,yes,md,mdp,part}"
See this option under Create and Build options.
+.TP
+.BR -b ", " --bitmap=
+Specify the bitmap file that was given when the array was created. If
+an array has an
+.B internal
+bitmap, there is no need to specify this when assembling the array.
+
+.TP
+.BR --backup-file=
+If
+.B --backup-file
+was used to grow the number of raid-devices in a RAID5, and the system
+crashed during the critical section, then the same
+.B --backup-file
+must be presented to --assemble to allow possibly corrupted data to be
+restored.
+
.TP
.BR -U ", " --update=
Update the superblock on each device while assembling the array. The
argument given to this flag can be one of
.BR sparc2.2 ,
.BR summaries ,
+.BR uuid ,
+.BR name ,
+.BR homehost ,
.BR resync ,
+.BR byteorder ,
+.BR devicesize ,
or
.BR super-minor .
The
.B sparc2.2
-option will adjust the superblock of an array what was created on a Sparc
+option will adjust the superblock of an array what was created on a Sparc
machine running a patched 2.2 Linux kernel. This kernel got the
alignment of part of the superblock wrong. You can use the
.B "--examine --sparc2.2"
The
.B super-minor
option will update the
-.B "prefered minor"
+.B "preferred minor"
field on each superblock to match the minor number of the array being
-assembled. This is not needed on 2.6 and later kernels as they make
-this adjustment automatically.
+assembled.
+This can be useful if
+.B --examine
+reports a different "Preferred Minor" to
+.BR --detail .
+In some cases this update will be performed automatically
+by the kernel driver. In particular the update happens automatically
+at the first write to an array with redundancy (RAID level 1 or
+greater) on a 2.6 (or later) kernel.
+
+The
+.B uuid
+option will change the uuid of the array. If a UUID is given with the
+"--uuid" option that UUID will be used as a new UUID and will
+.B NOT
+be used to help identify the devices in the array.
+If no "--uuid" is given, a random uuid is chosen.
+
+The
+.B name
+option will change the
+.I name
+of the array as stored in the superblock. This is only supported for
+version-1 superblocks.
+
+The
+.B homehost
+option will change the
+.I homehost
+as recorded in the superblock. For version-0 superblocks, this is the
+same as updating the UUID.
+For version-1 superblocks, this involves updating the name.
The
.B resync
to perform a "resync" pass to make sure that all redundant information
is correct.
+The
+.B byteorder
+option allows arrays to be moved between machines with different
+byte-order.
+When assembling such an array for the first time after a move, giving
+.B "--update=byteorder"
+will cause
+.I mdadm
+to expect superblocks to have their byteorder reversed, and will
+correct that order before assembling the array. This is only valid
+with original (Version 0.90) superblocks.
+
The
.B summaries
option will correct the summaries in the superblock. That is the
counts of total, working, active, failed, and spare devices.
+The
+.B devicesize
+will rarely be of use. It applies to version 1.1 and 1.2 metadata
+only (where the metadata is at the start of the device) and is only
+useful when the component device has changed size (typically become
+larger). The version 1 metadata records the amount of the device that
+can be used to store data, so if a device in a version 1.1 or 1.2
+array becomes larger, the metadata will still be visible, but the
+extra space will not. In this case it might be useful to assemble the
+array with
+.BR --update=devicesize .
+This will cause
+.I mdadm
+to determine the maximum usable amount of space on each device and
+update the relevant field in the metadata.
+
+.TP
+.B --auto-update-homehost
+This flag is only meaning with auto-assembly (see discussion below).
+In that situation, if no suitable arrays are found for this homehost,
+.I mdadm
+will recan for any arrays at all and will assemble them and update the
+homehost to match the current host.
+
.SH For Manage mode:
.TP
.BR -a ", " --add
-'''add, or
-hotadd listed devices.
+hot-add listed devices.
+
+.TP
+.BR --re-add
+re-add a device that was recently removed from an array.
.TP
.BR -r ", " --remove
.BR --set-faulty
same as --fail.
-.SH For Examine mode:
+.P
+Each of these options require that the first device list is the array
+to be acted upon and the remainder are component devices to be added,
+removed, or marked as fault. Several different operations can be
+specified for different devices, e.g.
+.in +5
+mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
+.in -5
+Each operation applies to all devices listed until the next
+operations.
+
+If an array is using a write-intent bitmap, then devices which have
+been removed can be re-added in a way that avoids a full
+reconstruction but instead just updated the blocks that have changed
+since the device was removed. For arrays with persistent metadata
+(superblocks) this is done automatically. For arrays created with
+.B --build
+mdadm needs to be told that this device we removed recently with
+.B --re-add.
+
+Devices can only be removed from an array if they are not in active
+use. i.e. that must be spares or failed devices. To remove an active
+device, it must be marked as
+.B faulty
+first.
+
+.SH For Misc mode:
+.TP
+.BR -Q ", " --query
+Examine a device to see
+(1) if it is an md device and (2) if it is a component of an md
+array.
+Information about what is discovered is presented.
+
+.TP
+.BR -D ", " --detail
+Print detail of one or more md devices.
+
+.TP
+.BR -E ", " --examine
+Print content of md superblock on device(s).
.TP
.B --sparc2.2
-In an array was created on a 2.2 Linux kernel patched with RAID
+If an array was created on a 2.2 Linux kernel patched with RAID
support, the superblock will have been created incorrectly, or at
least incompatibly with 2.4 and later kernels. Using the
.B --sparc2.2
the right thing, then the array can be successfully assembled using
.BR "--assemble --update=sparc2.2" .
-.SH For Misc mode:
+.TP
+.BR -X ", " --examine-bitmap
+Report information about a bitmap file.
.TP
.BR -R ", " --run
.BR -p ", " --program ", " --alert
Give a program to be run whenever an event is detected.
+.TP
+.BR -y ", " --syslog
+Cause all events to be reported through 'syslog'. The messages have
+facility of 'daemon' and varying priorities.
+
.TP
.BR -d ", " --delay
Give a delay in seconds.
.B NewArray
events and more significantly
.B DegradedArray
+and
+.B SparesMissing
events. Running
.in +5
.B " mdadm --monitor --scan -1"
.B TestMessage
alert for every array found at startup. This alert gets mailed and
passed to the alert program. This can be used for testing that alert
-message to get through successfully.
+message do get through successfully.
.SH ASSEMBLE MODE
.B --scan
was given and identify information is extracted from the configuration file.
-The identity can be given with the
+The identity can be given with the
.B --uuid
option, with the
.B --super-minor
option, can be found in the config file, or will be taken from the
super block on the first component-device listed on the command line.
-Devices can be given on the
+Devices can be given on the
.B --assemble
command line or in the config file. Only devices which have an md
superblock which contains the right identity will be considered for
any array.
-The config file is only used if explicitly named with
+The config file is only used if explicitly named with
.B --config
or requested with (a possibly implicit)
-.B --scan.
+.B --scan.
In the later case,
.B /etc/mdadm.conf
is used.
-If
+If
.B --scan
is not given, then the config file will only be used to find the
identity of md arrays.
is not given and insufficient drives were listed to start a complete
(non-degraded) array, then the array is not started (to guard against
usage errors). To insist that the array be started in this case (as
-may work for RAID1, 4, 5 or 6), give the
+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
-.I mdadm
-will create the md device if necessary or will re-create it if it
-doesn't look usable as it is.
+If the md device does not exist, then it will be created providing the
+intent is clear. i.e. the name must be in a standard form, or the
+.I --auto
+option must be given to clarify how and whether the device should be
+created.
This can be useful for handling partitioned devices (which don't have
a stable device number - it can change after a reboot) and when using
If the option to "auto" is "mdp" or "part" or (on the command line
only) "p", then mdadm will create a partitionable array, using the
-first free one that is not inuse, and does not already have an entry
+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)
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
+string to the device name, with an intervening "p" if the device name
ends with a digit.
The
not use a config file, the "auto=" config option does not apply to
these modes.
+.SS Auto Assembly
+When
+.B --assemble
+is used with
+.B --scan
+and no devices are listed,
+.I mdadm
+will first attempt to assemble all the arrays listed in the config
+file.
+
+If a
+.B homehost
+has been specified (either in the config file or on the command line),
+.I mdadm
+will look further for possible arrays and will try to assemble
+anything that it finds which is tagged as belonging to the given
+homehost. This is the only situation where
+.I mdadm
+will assemble arrays without being given specific device name or
+identify information for the array.
+
+If
+.I mdadm
+finds a consistent set of devices that look like they should comprise
+an array, and if the superblock is tagged as belonging to the given
+home host, it will automatically choose a device name and try to
+assemble the array. If the array uses version-0.90 metadata, then the
+.B minor
+number as recorded in the superblock is used to create a name in
+.B /dev/md/
+so for example
+.BR /dev/md/3 .
+If the array uses version-1 metadata, then the
+.B name
+from the superblock is used to similarly create a name in
+.BR /dev/md .
+The name will have any 'host' prefix stripped first.
+
+If
+.I mdadm
+cannot find any array for the given host at all, and if
+.B --auto-update-homehost
+is given, then
+.I mdadm
+will search again for any array (not just an array created for this
+host) and will assemble each assuming
+.IR --update=homehost .
+This will change the host tag in the superblock so that on the next run,
+these arrays will be found without the second pass. The intention of
+this feature is to support transitioning a set of md arrays to using
+homehost tagging.
+
+The reason for requiring arrays to be tagged with the homehost for
+auto assembly is to guard against problems that can arise when moving
+devices from one host to another.
+
.SH BUILD MODE
.HP 12
.I devices
.PP
-This usage is similar to
+This usage is similar to
.BR --create .
-The difference is that it creates a legacy array without a superblock. With
+The difference is that it creates an array without a superblock. With
these arrays there is no difference between initially creating the array and
subsequently assembling the array, except that hopefully there is useful
data there in the second case.
-The level may only be 0, raid0, or linear. All devices must be listed
-and the array will be started once complete.
+The level may raid0, linear, multipath, or faulty, or one of their
+synonyms. All devices must be listed and the array will be started
+once complete.
.SH CREATE MODE
This usage will initialise a new md array, associate some devices with
it, and activate the array.
-This the
+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 size exceeds 1%.
If any discrepancy is found, the array will not automatically be run, though
-the presence of a
+the presence of a
.B --run
can override this caution.
.I --force
option.
-'''If the
+When creating an array with version-1 metadata a name for the host is
+required.
+If this is not given with the
+.B --name
+option,
+.I mdadm
+will chose a name based on the last component of the name of the
+device being created. So if
+.B /dev/md3
+is being created, then the name
+.B 3
+will be chosen.
+If
+.B /dev/md/home
+is being created, then the name
+.B home
+will be used.
+
+'''If the
'''.B --size
'''option is given, it is not necessary to list any component-devices in this command.
'''They can be added later, before a
-'''.B --run.
-'''If no
+'''.B --run.
+'''If no
'''.B --size
'''is given, the apparent size of the smallest drive given is used.
.B --readonly
start the array readonly - not supported yet.
+
.SH MANAGE MODE
.HP 12
Usage:
.B /dev/md0
and will then remove it from the array and finally add it back
in as a spare. However only one md array can be affected by a single
-command.
+command.
.SH MISC MODE
.HP 12
may move a spare drive from one array to another if they are in the
same
.B spare-group
-and if the destination array has a failed drive but not spares.
+and if the destination array has a failed drive but no spares.
If any devices are listed on the command line,
.B mdadm
be mailed to a given E-mail address.
When passing event to program, the program is run once for each event
-and is given 2 or 3 command-line arguements. The first is the
+and is given 2 or 3 command-line arguments. The first is the
name of the event (see below). The second is the name of the
md device which is affected, and the third is the name of a related
device if relevant, such as a component device that has failed.
.TP
.B DeviceDisappeared
An md array which previously was configured appears to no longer be
-configured.
+configured. (syslog priority: Critical)
+
+If
+.I mdadm
+was told to monitor an array which is RAID0 or Linear, then it will
+report
+.B DeviceDisappeared
+with the extra information
+.BR Wrong-Level .
+This is because RAID0 and Linear do not support the device-failed,
+hot-spare and resync operations which are monitored.
.TP
.B RebuildStarted
-An md array started reconstruction.
+An md array started reconstruction. (syslog priority: Warning)
.TP
.BI Rebuild NN
Where
.I NN
is 20, 40, 60, or 80, this indicates that rebuild has passed that many
-percentage of the total.
+percentage of the total. (syslog priority: Warning)
.TP
.B RebuildFinished
An md array that was rebuilding, isn't any more, either because it
-finished normally or was aborted.
+finished normally or was aborted. (syslog priority: Warning)
.TP
.B Fail
-An active component device of an array has been marked as faulty.
+An active component device of an array has been marked as
+faulty. (syslog priority: Critical)
.TP
.B FailSpare
A spare component device which was being rebuilt to replace a faulty
-device has failed.
+device has failed. (syslog priority: Critial)
.TP
.B SpareActive
A spare component device which was being rebuilt to replace a faulty
-device as been successfully rebuild and has been made active.
+device has been successfully rebuilt and has been made active.
+(syslog priority: Info)
.TP
.B NewArray
A new md array has been detected in the
.B /proc/mdstat
-file.
+file. (syslog priority: Info)
.TP
.B DegradedArray
notices a drive failure which causes degradation, but only when
.I mdadm
notices that an array is degraded when it first sees the array.
+(syslog priority: Critial)
.TP
.B MoveSpare
A spare drive has been moved from one array in a
.B spare-group
to another to allow a failed drive to be replaced.
+(syslog priority: Info)
+
+.TP
+.B SparesMissing
+If
+.I mdadm
+has been told, via the config file, that an array should have a certain
+number of spare devices, and
+.I mdadm
+detects that it has fewer that this number when it first sees the
+array, it will report a
+.B SparesMissing
+message.
+(syslog priority: Warning)
.TP
.B TestMessage
An array was found at startup, and the
.B --test
flag was given.
+(syslog priority: Info)
.RE
Only
.B Fail ,
.B FailSpare ,
.B DegradedArray ,
+.B SparesMissing ,
and
.B TestMessage
cause Email to be sent. All events cause the program to be run.
The GROW mode is used for changing the size or shape of an active
array.
For this to work, the kernel must support the necessary change.
-Various types of growth may be added during 2.6 development, possibly
+Various types of growth are being added during 2.6 development,
including restructuring a raid5 array to have more active devices.
-Currently the only support available is to change the "size" attribute
-for arrays with redundancy, and the raid-disks attribute of RAID1
-arrays.
+Currently the only support available is to
+.IP \(bu 4
+change the "size" attribute
+for RAID1, RAID5 and RAID6.
+.IP \(bu 4
+increase the "raid-disks" attribute of RAID1 and RAID5.
+.IP \(bu 4
+add a write-intent bitmap to any array which support these bitmaps, or
+remove a write-intent bitmap from such an array.
+.PP
-Normally when an array is build the "size" it taken from the smallest
+.SS SIZE CHANGES
+Normally when an array is built the "size" it taken from the smallest
of the drives. If all the small drives in an arrays are, one at a
time, removed and replaced with larger drives, then you could have an
array of large drives with only a small amount used. In this
stored in the array will not automatically grow to use the space. The
filesystem will need to be explicitly told to use the extra space.
+.SS RAID-DEVICES CHANGES
+
A RAID1 array can work with any number of devices from 1 upwards
(though 1 is not very useful). There may be times which you want to
increase or decrease the number of active devices. Note that this is
devices that which were in those slots must be failed and removed.
When the number of devices is increased, any hot spares that are
-present may be activated immediately.
+present will be activated immediately.
+
+Increasing the number of active devices in a RAID5 is much more
+effort. Every block in the array will need to be read and written
+back to a new location. From 2.6.17, the Linux Kernel is able to do
+this safely, including restart and interrupted "reshape".
+
+When relocating the first few stripes on a raid5, it is not possible
+to keep the data on disk completely consistent and crash-proof. To
+provide the required safety, mdadm disables writes to the array while
+this "critical section" is reshaped, and takes a backup of the data
+that is in that section. This backup is normally stored in any spare
+devices that the array has, however it can also be stored in a
+separate file specified with the
+.B --backup-file
+option. If this option is used, and the system does crash during the
+critical period, the same file must be passed to
+.B --assemble
+to restore the backup and reassemble the array.
+
+.SS BITMAP CHANGES
+
+A write-intent bitmap can be added to, or removed from, an active
+array. Either internal bitmaps, or bitmaps stored in a separate file
+can be added. Note that if you add a bitmap stored in a file which is
+in a filesystem that is on the raid array being affected, the system
+will deadlock. The bitmap must be on a separate filesystem.
.SH EXAMPLES
.B " mdadm --assemble --scan"
.br
-This will assemble and start all arrays listed in the standard confile
+This will assemble and start all arrays listed in the standard config file
file. This command will typically go in a system startup file.
.B " mdadm --stop --scan"
.br
.B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
.ber
-This will find what arrays could be assembled from existign IDE and
+This will find what arrays could be assembled from existing IDE and
SCSI whole drives (not partitions) and store the information is the
format of a config file.
This file is very likely to contain unwanted detail, particularly
.B " mdadm --create --help"
.br
-Providew help about the Create mode.
+Provide help about the Create mode.
.B " mdadm --config --help"
.br
.SS /proc/mdstat
-If you're using the
-.B /proc
+If you're using the
+.B /proc
filesystem,
.B /proc/mdstat
lists all active md devices with information about them.
.B mdadm
was previously known as
.BR mdctl .
-
+.P
+.B mdadm
+is completely separate from the
+.B raidtools
+package, and does not use the
+.I /etc/raidtab
+configuration file at all.
+
.SH SEE ALSO
For information on the various levels of
RAID, check out:
.UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
.UE
+'''.PP
+'''for new releases of the RAID driver check out:
+'''
+'''.IP
+'''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
+'''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
+'''.UE
+'''.PP
+'''or
+'''.IP
+'''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
+'''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
+'''.UE
.PP
-for new releases of the RAID driver check out:
-
+The latest version of
+.I mdadm
+should always be available from
.IP
-.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
-ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
+.UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
+http://www.kernel.org/pub/linux/utils/raid/mdadm/
.UE
.PP
-or
-.IP
-.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
-http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
-.URk
-.PP
-.BR mdadm.conf (5),
-.BR md (4).
+.IR mdadm.conf (5),
+.IR md (4).
.PP
.IR raidtab (5),
.IR raid0run (8),
.IR raidstop (8),
-.IR mkraid (8)
+.IR mkraid (8).
projects / thirdparty / mdadm.git / blobdiff