4 mdadm \- manage MD devices
10 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
13 RAID devices are virtual devices created from two or more
14 real block devices. This allows multiple devices (typically disk
15 drives or partitions there-of) to be combined into a single device to
16 hold (for example) a single filesystem.
17 Some RAID levels include redundancy and so can survive some degree of
20 Linux Software RAID devices are implemented through the md (Multiple
21 Devices) device driver.
23 Currently, Linux supports
35 .B MULTIPATH is not a Software RAID mechanism, but does involve
38 each device is a path to one common physical storage device.
42 is a program that can be used to create, manage, and monitor
44 such it provides a similar set of functionality to the
47 The key differences between
54 is a single program and not a collection of programs.
57 can perform (almost) all of its functions without having a
58 configuration file and does not use one by default. Also
60 helps with management of the configuration
64 can provide information about your arrays (through Query, Detail, and Examine)
74 configuration file, at all. It has a different configuration file
75 with a different format and an different purpose.
78 mdadm has 6 major modes of operation:
81 Assemble the parts of a previously created
82 array into an active array. Components can be explicitly given
83 or can be searched for.
85 checks that the components
86 do form a bona fide array, and can, on request, fiddle superblock
87 information so as to assemble a faulty array.
91 Build a legacy array without per-device superblocks.
95 Create a new array with per-device superblocks.
97 '''in several step create-add-add-run or it can all happen with one command.
101 This is for doing things to specific components of an array such as
102 adding new spares and removing faulty devices.
106 This mode allows operations on independent devices such as examine MD
107 superblocks, erasing old superblocks and stopping active arrays.
110 .B "Follow or Monitor"
111 Monitor one or more md devices and act on any state changes. This is
112 only meaningful for raid1, raid5 or multipath arrays as only these have
113 interesting state. raid0 or linear never have missing, spare, or
114 failed drives, so there is nothing to monitor.
119 Available options are:
122 .BR -A ", " --assemble
123 Assemble a pre-existing array.
127 Build a legacy array without superblocks.
135 Examine a device to see
136 (1) if it is an md device and (2) if it is a component of an md
138 Information about what is discovered is presented.
142 Print detail of one or more md devices.
145 .BR -E ", " --examine
146 Print content of md superblock on device(s).
149 .BR -F ", " --follow ", " --monitor
156 Display help message or, after above option, mode specific help
161 Display more detailed help about command line parsing and some commonly
165 .BR -V ", " --version
166 Print version information for mdadm.
169 .BR -v ", " --verbose
170 Be more verbose about what is happening.
174 Be less verbose. This is used with
181 Be more forceful about certain operations. See the various modes of
182 the exact meaning of this option in different contexts.
185 .BR -c ", " --config=
186 Specify the config file. Default is
187 .BR /etc/mdadm.conf .
188 If the config file given is
190 then nothing will be read, but
192 will act as though the config file contained exactly
193 .B "DEVICE partitions"
196 to find a list of devices to scan.
199 is given for the config file, then
201 will act as though the config file were empty.
207 for missing information.
208 In general, this option gives
210 permission to get any missing information, like component devices,
211 array devices, array identities, and alert destination from the
213 .BR /etc/mdadm.conf .
214 One exception is MISC mode when using
220 says to get a list of array devices from
223 .SH For create or build:
227 Specify chunk size of kibibytes. The default is 64.
231 Specify rounding factor for linear array (==chunk size)
235 Set raid level. Options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid5, 4,
236 raid5, 5, multipath, mp. Obviously some of these are synonymous.
237 Only the first 4 are valid when Building.
240 .BR -p ", " --parity=
241 Set raid5 parity algorithm. Options are:
246 la, ra, ls, rs. The default is left-symmetric.
253 .BR -n ", " --raid-devices=
254 Specify the number of active devices in the array. This, plus the
255 number of spare devices (see below) must equal the number of
257 (including "\fBmissing\fP" devices)
258 that are listed on the command line.
261 .BR -x ", " --spare-devices=
262 Specify the number of spare (eXtra) devices in the initial array.
263 Spares can also be added
264 and removed later. The number of component devices listed
265 on the command line must equal the number of raid devices plus the
266 number of spare devices.
271 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5.
272 This must be a multiple of the chunk size, and must leave about 128Kb
273 of space at the end of the drive for the RAID superblock.
274 If this is not specified
275 (as it normally is not) the smallest drive (or partition) sets the
276 size, though if there is a variance among the drives of greater than 1%, a warning is
283 uuid of array to assemble. Devices which don't have this uuid are
287 .BR -m ", " --super-minor=
288 Minor number of device that array was created for. Devices which
289 don't have this minor number are excluded. If you create an array as
290 /dev/md1, then all superblocks will contain the minor number 1, even if
291 the array is later assembled as /dev/md2.
293 Giving the literal word "dev" for
297 to use the minor number of the md device that is being assembled.
301 will look for super blocks with a minor number of 0.
305 Assemble the array even if some superblocks appear out-of-date
309 Attempt to start the array even if fewer drives were given than are
310 needed for a full array. Normally if not all drives are found and
312 is not used, then the array will be assembled but not started.
315 an attempt will be made to start it anyway.
318 .BR -U ", " --update=
319 Update the superblock on each device while assembling the array. The
320 argument given to this flag can be either
327 option will adjust the superblock of an array what was created on a Sparc
328 machine running a patched 2.2 Linux kernel. This kernel got the
329 alignment of part of the superblock wrong. You can use the
330 .B "--examine --sparc2.2"
333 to see what effect this would have.
337 option will update the
339 field on each superblock to match the minor number of the array being
340 assembled. This is not need on 2.6 and later kernels as they make
341 this adjustment automatically.
349 hotadd listed devices.
353 remove listed devices. They must not be active. i.e. they should
354 be failed or spare devices.
358 mark listed devices as faulty.
364 .SH For Examine mode:
368 In an array was created on a 2.2 Linux kernel patched with RAID
369 support, the superblock will have been created incorrectly, or at
370 least incompatibly with 2.4 and later kernels. Using the
374 will fix the superblock before displaying it. If this appears to do
375 the right thing, then the array can be successfully assembled using
376 .BR "--assemble --update=sparc2.2" .
382 start a partially built array.
386 deactivate array, releasing all resources.
389 .BR -o ", " --readonly
390 mark array as readonly.
393 .BR -w ", " --readwrite
394 mark array as readwrite.
398 If the device contains a valid md superblock, the block is
399 over-written with zeros. With
401 the block where the superblock would be is over-written even if it
402 doesn't appear to be valid.
404 .SH For Monitor mode:
407 Give a mail address to send alerts to.
410 .BR -p ", " --program ", " --alert
411 Give a program to be run whenever an event is detected.
415 Give a delay in seconds.
417 polls the md arrays and then waits this many seconds before polling
418 again. The default is 60 seconds.
421 .BR -f ", " --daemonise
424 to run as a background daemon if it decides to monitor anything. This
425 causes it to fork and run in the child, and to disconnect form the
426 terminal. The process id of the child is written to stdout.
429 which will only continue monitoring if a mail address or alert program
430 is found in the config file.
437 .I md-device options-and-component-devices...
440 .B mdadm --assemble --scan
441 .I md-devices-and-options...
444 .B mdadm --assemble --scan
448 This usage assembles one or more raid arrays from pre-existing components.
449 For each array, mdadm needs to know the md device, the identity of the
450 array, and a number of component-devices. These can be found in a number of ways.
452 In the first usage example (without the
454 the first device given is the md device.
455 In the second usage example, all devices listed are treated as md
456 devices and assembly is attempted.
457 In the third (where no devices are listed) all md devices that are
458 listed in the configuration file are assembled.
460 If precisely one device is listed, but
466 was given and identify information is extracted from the configuration file.
468 The identity can be given with the
472 option, can be found in the config file, or will be taken from the
473 super block on the first component-device listed on the command line.
475 Devices can be given on the
477 command line or in the config file. Only devices which have an md
478 superblock which contains the right identity will be considered for
481 The config file is only used if explicitly named with
483 or requested with (a possibly implicit)
491 is not given, then the config file will only be used to find the
492 identity of md arrays.
494 Normally the array will be started after it is assembled. However if
496 is not given and insufficient drives were listed to start a complete
497 (non-degraded) array, then the array is not started (to guard against
498 usage errors). To insist that the array be started in this case (as
499 may work for RAID1 or RAID5), give the
512 .BI --raid-devices= Z
516 This usage is similar to
518 The difference is that it creates a legacy array without a superblock. With
519 these arrays there is no difference between initially creating the array and
520 subsequently assembling the array, except that hopefully there is useful
521 data there in the second case.
523 The level may only be 0, raid0, or linear. All devices must be listed
524 and the array will be started once complete.
535 .BI --raid-devices= Z
539 This usage will initialise a new md array, associate some devices with
540 it, and activate the array.
542 As devices are added, they are checked to see if they contain raid
543 superblocks or filesystems. They are also checked to see if the variance in
544 device size exceeds 1%.
546 If any discrepancy is found, the array will not automatically be run, though
549 can override this caution.
551 To create a "degraded" array in which some devices are missing, simply
552 give the word "\fBmissing\fP"
553 in place of a device name. This will cause
555 to leave the corresponding slot in the array empty.
556 For a RAID4 or RAID5 array at most one slot can be
558 For a RAID1 array, only one real device needs to be given. All of the
564 '''option is given, it is not necessary to list any component-devices in this command.
565 '''They can be added later, before a
569 '''is given, the apparent size of the smallest drive given is used.
571 The General Management options that are valid with --create are:
574 insist of running the array even if some devices look like they might
579 start the array readonly - not supported yet.
586 .I options... devices...
589 This usage will allow individual devices in an array to be failed,
590 removed or added. It is possible to perform multiple operations with
591 on command. For example:
593 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
599 and will then remove it from the array and finally add it back
600 in as a spare. However only one md array can be affected by a single
611 MISC mode includes a number if distinct operations that
612 operate on distinct devices. The operations are:
615 The device is examined to see if it is
616 (1) an active md array, or
617 (2) a component of an md array.
618 The information discovered is reported.
622 The device should be an active md device.
624 will display a detailed description of the array.
628 will cause the output to be less detailed and the format to be
629 suitable for inclusion in
630 .BR /etc/mdadm.conf .
634 The device should be a component of an md array.
636 will read the md superblock of the device and display the contents.
641 then multiple devices that are components of the one array
642 are grouped together and reported in a single entry suitable
644 .BR /etc/mdadm.conf .
648 without listing any devices will cause all devices listed in the
649 config file to be examined.
653 This devices should active md arrays which will be deactivated, if
654 they are not currently in use.
658 This will fully activate a partially assembled md array.
662 This will mark an active array as read-only, providing that it is
663 not currently being used.
669 array back to being read/write.
673 For all operations except
676 will cause the operation to be applied to all arrays listed in
681 causes all devices listed in the config file to be examined.
689 .I options... devices...
694 to periodically poll a number of md arrays and to report on any events
697 will never exit once it decides that there are arrays to be checked,
698 so it should normally be run in the background.
700 As well as reporting events,
702 may move a spare drive from one array to another if they are in the
705 and if the destination array has a failed drive but not spares.
707 If any devices are listed on the command line,
709 will only monitor those devices. Otherwise all arrays listed in the
710 configuration file will be monitored. Further, if
712 is given, then any other md devices that appear in
714 will also be monitored.
716 The result of monitoring the arrays is the generation of events.
717 These events are passed to a separate program (if specified) and may
718 be mailed to a given E-mail address.
720 When passing event to program, the program is run once for each event
721 and is given 2 or 3 command-line arguements. The first is the
722 name of the event (see below). The second is the name of the
723 md device which is affected, and the third is the name of a related
724 device if relevant, such as a component device that has failed.
728 is given, then a program or an E-mail address must be specified on the
729 command line or in the config file. If neither are available, then
731 will not monitor anything.
735 will continue monitoring as long as something was found to monitor. If
736 no program or email is given, then each event is reported to
739 The different events are:
744 An md array which previously was configured appears to no longer be
749 An md array started reconstruction.
755 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
756 percentage of the total.
760 An active component device of an array has been marked as faulty.
764 A spare component device which was being rebuilt to replace a faulty
769 A spare component device which was being rebuilt to replace a faulty
770 device as been successfully rebuild and has been made active.
774 A new md array has been detected in the
780 A spare drive has been moved from one array in a
782 to another to allow a failed drive to be replaced.
790 cause Email to be sent. All events cause the program to be run.
791 The program is run with two or three arguments, they being the event
792 name, the array device and possibly a second device.
794 Each event has an associated array device (e.g.
796 and possibly a second device. For
801 the second device is the relevant component device.
804 the second device is the array that the spare was moved from.
808 to move spares from one array to another, the different arrays need to
809 be labelled with the same
811 in the configuration file. The
813 name can be any string. It is only necessary that different spare
814 groups use different names.
818 detects that an array which is in a spare group has fewer active
819 devices than necessary for the complete array, and has no spare
820 devices, it will look for another array in the same spare group that
821 has a full complement of working drive and a spare. It will then
822 attempt to remove the spare from the second drive and add it to the
824 If the removal succeeds but the adding fails, then it is added back to
829 .B " mdadm --query /dev/name-of-device"
831 This will find out if a given device is a raid array, or is part of
832 one, and will provide brief information about the device.
834 .B " mdadm --assemble --scan"
836 This will assemble and start all arrays listed in the standard confile
837 file. This command will typically go in a system startup file.
839 .B " mdadm --stop --scan"
841 This will shut down all array that can be shut down (i.e. are not
842 currently in used). This will typically going in a system shutdown script.
844 .B " mdadm --follow --scan --delay=120"
846 If (and only if) there is an Email address or program given in the
847 standard config file, then
848 monitor the status of all arrays listed in that file by
849 polling them ever 2 minutes.
851 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
853 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
856 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
858 .B " mdadm --detail --scan >> mdadm.conf"
860 This will create a prototype config file that describes currently
861 active arrays that are known to be made from partitions of IDE or SCSI drives.
862 This file should be reviewed before being used as it may
863 contain unwanted detail.
865 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
867 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
869 This will find what arrays could be assembled from existign IDE and
870 SCSI whole drives (not partitions) and store the information is the
871 format of a config file.
872 This file is very likely to contain unwanted detail, particularly
875 entries. It should be reviewed and edited before being used as an
878 .B " mdadm --examine --brief --scan --config=partitions"
880 .B " mdadm -Ebsc partitions"
882 Create a list of devices by reading
883 .BR /proc/partitions ,
884 scan these for RAID superblocks, and printout a brief listing of all
887 .B " mdadm -Ac partitions -m 0 /dev/md0"
889 Scan all partitions and devices listed in
893 out of all such devices with a RAID superblock with a minor number of 0.
895 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
897 If config file contains a mail address or alert program, run mdadm in
898 the background in monitor mode monitoring all md devices. Also write
899 pid of mdadm daemon to
902 .B " mdadm --create --help"
904 Providew help about the Create mode.
906 .B " mdadm --config --help"
908 Provide help about the format of the config file.
912 Provide general help.
923 lists all active md devices with information about them.
925 uses this to find arrays when
927 is given in Misc mode, and to monitor array reconstruction
933 The config file lists which devices may be scanned to see if
934 they contain MD super block, and gives identifying information
935 (e.g. UUID) about known MD arrays. See
942 was previously known as
946 For information on the various levels of
950 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
951 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
954 for new releases of the RAID driver check out:
957 .UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
958 ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
963 .UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
964 http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
projects / thirdparty / mdadm.git / blob