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. When used with
237 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid5, 4,
238 raid5, 5, multipath, mp. Obviously some of these are synonymous.
242 only linear, raid0, 0, stripe are valid.
245 .BR -p ", " --parity=
246 Set raid5 parity algorithm. Options are:
251 la, ra, ls, rs. The default is left-symmetric.
258 .BR -n ", " --raid-devices=
259 Specify the number of active devices in the array. This, plus the
260 number of spare devices (see below) must equal the number of
262 (including "\fBmissing\fP" devices)
263 that are listed on the command line. Setting a value of 1 is probably
264 a mistake and so requires that
266 be specified first. A value of 1 will then be allowed for linear,
267 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
269 Note that this number cannot be changed once the array has been created.
272 .BR -x ", " --spare-devices=
273 Specify the number of spare (eXtra) devices in the initial array.
274 Spares can also be added
275 and removed later. The number of component devices listed
276 on the command line must equal the number of raid devices plus the
277 number of spare devices.
282 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5.
283 This must be a multiple of the chunk size, and must leave about 128Kb
284 of space at the end of the drive for the RAID superblock.
285 If this is not specified
286 (as it normally is not) the smallest drive (or partition) sets the
287 size, though if there is a variance among the drives of greater than 1%, a warning is
294 uuid of array to assemble. Devices which don't have this uuid are
298 .BR -m ", " --super-minor=
299 Minor number of device that array was created for. Devices which
300 don't have this minor number are excluded. If you create an array as
301 /dev/md1, then all superblocks will contain the minor number 1, even if
302 the array is later assembled as /dev/md2.
304 Giving the literal word "dev" for
308 to use the minor number of the md device that is being assembled.
312 will look for super blocks with a minor number of 0.
316 Assemble the array even if some superblocks appear out-of-date
320 Attempt to start the array even if fewer drives were given than are
321 needed for a full array. Normally if not all drives are found and
323 is not used, then the array will be assembled but not started.
326 an attempt will be made to start it anyway.
329 .BR -U ", " --update=
330 Update the superblock on each device while assembling the array. The
331 argument given to this flag can be one of
339 option will adjust the superblock of an array what was created on a Sparc
340 machine running a patched 2.2 Linux kernel. This kernel got the
341 alignment of part of the superblock wrong. You can use the
342 .B "--examine --sparc2.2"
345 to see what effect this would have.
349 option will update the
351 field on each superblock to match the minor number of the array being
352 assembled. This is not needed on 2.6 and later kernels as they make
353 this adjustment automatically.
357 option will correct the summaries in the superblock. That is the
358 counts of total, working, active, failed, and spare devices.
365 hotadd listed devices.
369 remove listed devices. They must not be active. i.e. they should
370 be failed or spare devices.
374 mark listed devices as faulty.
380 .SH For Examine mode:
384 In an array was created on a 2.2 Linux kernel patched with RAID
385 support, the superblock will have been created incorrectly, or at
386 least incompatibly with 2.4 and later kernels. Using the
390 will fix the superblock before displaying it. If this appears to do
391 the right thing, then the array can be successfully assembled using
392 .BR "--assemble --update=sparc2.2" .
398 start a partially built array.
402 deactivate array, releasing all resources.
405 .BR -o ", " --readonly
406 mark array as readonly.
409 .BR -w ", " --readwrite
410 mark array as readwrite.
414 If the device contains a valid md superblock, the block is
415 over-written with zeros. With
417 the block where the superblock would be is over-written even if it
418 doesn't appear to be valid.
426 is set to reflect the status of the device.
428 .SH For Monitor mode:
431 Give a mail address to send alerts to.
434 .BR -p ", " --program ", " --alert
435 Give a program to be run whenever an event is detected.
439 Give a delay in seconds.
441 polls the md arrays and then waits this many seconds before polling
442 again. The default is 60 seconds.
445 .BR -f ", " --daemonise
448 to run as a background daemon if it decides to monitor anything. This
449 causes it to fork and run in the child, and to disconnect form the
450 terminal. The process id of the child is written to stdout.
453 which will only continue monitoring if a mail address or alert program
454 is found in the config file.
457 .BR -1 ", " --oneshot
458 Check arrays only once. This will generate
460 events and more significantly
464 .B " mdadm --monitor --scan -1"
466 from a cron script will ensure regular notification of any degraded arrays.
473 .I md-device options-and-component-devices...
476 .B mdadm --assemble --scan
477 .I md-devices-and-options...
480 .B mdadm --assemble --scan
484 This usage assembles one or more raid arrays from pre-existing components.
485 For each array, mdadm needs to know the md device, the identity of the
486 array, and a number of component-devices. These can be found in a number of ways.
488 In the first usage example (without the
490 the first device given is the md device.
491 In the second usage example, all devices listed are treated as md
492 devices and assembly is attempted.
493 In the third (where no devices are listed) all md devices that are
494 listed in the configuration file are assembled.
496 If precisely one device is listed, but
502 was given and identify information is extracted from the configuration file.
504 The identity can be given with the
508 option, can be found in the config file, or will be taken from the
509 super block on the first component-device listed on the command line.
511 Devices can be given on the
513 command line or in the config file. Only devices which have an md
514 superblock which contains the right identity will be considered for
517 The config file is only used if explicitly named with
519 or requested with (a possibly implicit)
527 is not given, then the config file will only be used to find the
528 identity of md arrays.
530 Normally the array will be started after it is assembled. However if
532 is not given and insufficient drives were listed to start a complete
533 (non-degraded) array, then the array is not started (to guard against
534 usage errors). To insist that the array be started in this case (as
535 may work for RAID1 or RAID5), give the
548 .BI --raid-devices= Z
552 This usage is similar to
554 The difference is that it creates a legacy array without a superblock. With
555 these arrays there is no difference between initially creating the array and
556 subsequently assembling the array, except that hopefully there is useful
557 data there in the second case.
559 The level may only be 0, raid0, or linear. All devices must be listed
560 and the array will be started once complete.
571 .BI --raid-devices= Z
575 This usage will initialise a new md array, associate some devices with
576 it, and activate the array.
578 As devices are added, they are checked to see if they contain raid
579 superblocks or filesystems. They are also checked to see if the variance in
580 device size exceeds 1%.
582 If any discrepancy is found, the array will not automatically be run, though
585 can override this caution.
587 To create a "degraded" array in which some devices are missing, simply
588 give the word "\fBmissing\fP"
589 in place of a device name. This will cause
591 to leave the corresponding slot in the array empty.
592 For a RAID4 or RAID5 array at most one slot can be
594 For a RAID1 array, only one real device needs to be given. All of the
598 When creating a RAID5 array,
600 will automatically create a degraded array with an extra spare drive.
601 This is because building the spare into a degraded array is in general faster than resyncing
602 the parity on a non-degraded, but not clean, array. This feature can
603 be over-ridden with the
609 '''option is given, it is not necessary to list any component-devices in this command.
610 '''They can be added later, before a
614 '''is given, the apparent size of the smallest drive given is used.
616 The General Management options that are valid with --create are:
619 insist of running the array even if some devices look like they might
624 start the array readonly - not supported yet.
631 .I options... devices...
634 This usage will allow individual devices in an array to be failed,
635 removed or added. It is possible to perform multiple operations with
636 on command. For example:
638 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
644 and will then remove it from the array and finally add it back
645 in as a spare. However only one md array can be affected by a single
656 MISC mode includes a number if distinct operations that
657 operate on distinct devices. The operations are:
660 The device is examined to see if it is
661 (1) an active md array, or
662 (2) a component of an md array.
663 The information discovered is reported.
667 The device should be an active md device.
669 will display a detailed description of the array.
673 will cause the output to be less detailed and the format to be
674 suitable for inclusion in
675 .BR /etc/mdadm.conf .
678 will normally be 0 unless
680 failed to get useful information about the device(s). However if the
682 option is given, then the exit status will be:
686 The array is functioning normally.
689 The array has at least one failed device.
692 The array has multiple failed devices and hence is unusable (raid4 or
696 There was an error while trying to get information about the device.
701 The device should be a component of an md array.
703 will read the md superblock of the device and display the contents.
708 then multiple devices that are components of the one array
709 are grouped together and reported in a single entry suitable
711 .BR /etc/mdadm.conf .
715 without listing any devices will cause all devices listed in the
716 config file to be examined.
720 This devices should active md arrays which will be deactivated, if
721 they are not currently in use.
725 This will fully activate a partially assembled md array.
729 This will mark an active array as read-only, providing that it is
730 not currently being used.
736 array back to being read/write.
740 For all operations except
743 will cause the operation to be applied to all arrays listed in
748 causes all devices listed in the config file to be examined.
756 .I options... devices...
761 to periodically poll a number of md arrays and to report on any events
764 will never exit once it decides that there are arrays to be checked,
765 so it should normally be run in the background.
767 As well as reporting events,
769 may move a spare drive from one array to another if they are in the
772 and if the destination array has a failed drive but not spares.
774 If any devices are listed on the command line,
776 will only monitor those devices. Otherwise all arrays listed in the
777 configuration file will be monitored. Further, if
779 is given, then any other md devices that appear in
781 will also be monitored.
783 The result of monitoring the arrays is the generation of events.
784 These events are passed to a separate program (if specified) and may
785 be mailed to a given E-mail address.
787 When passing event to program, the program is run once for each event
788 and is given 2 or 3 command-line arguements. The first is the
789 name of the event (see below). The second is the name of the
790 md device which is affected, and the third is the name of a related
791 device if relevant, such as a component device that has failed.
795 is given, then a program or an E-mail address must be specified on the
796 command line or in the config file. If neither are available, then
798 will not monitor anything.
802 will continue monitoring as long as something was found to monitor. If
803 no program or email is given, then each event is reported to
806 The different events are:
811 An md array which previously was configured appears to no longer be
816 An md array started reconstruction.
822 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
823 percentage of the total.
827 An active component device of an array has been marked as faulty.
831 A spare component device which was being rebuilt to replace a faulty
836 A spare component device which was being rebuilt to replace a faulty
837 device as been successfully rebuild and has been made active.
841 A new md array has been detected in the
847 A newly noticed array appears to be degraded. This message is not
850 notices a drive failure which causes degradation, but only when
852 notices that an array is degraded when it first sees the array.
856 A spare drive has been moved from one array in a
858 to another to allow a failed drive to be replaced.
866 cause Email to be sent. All events cause the program to be run.
867 The program is run with two or three arguments, they being the event
868 name, the array device and possibly a second device.
870 Each event has an associated array device (e.g.
872 and possibly a second device. For
877 the second device is the relevant component device.
880 the second device is the array that the spare was moved from.
884 to move spares from one array to another, the different arrays need to
885 be labelled with the same
887 in the configuration file. The
889 name can be any string. It is only necessary that different spare
890 groups use different names.
894 detects that an array which is in a spare group has fewer active
895 devices than necessary for the complete array, and has no spare
896 devices, it will look for another array in the same spare group that
897 has a full complement of working drive and a spare. It will then
898 attempt to remove the spare from the second drive and add it to the
900 If the removal succeeds but the adding fails, then it is added back to
905 .B " mdadm --query /dev/name-of-device"
907 This will find out if a given device is a raid array, or is part of
908 one, and will provide brief information about the device.
910 .B " mdadm --assemble --scan"
912 This will assemble and start all arrays listed in the standard confile
913 file. This command will typically go in a system startup file.
915 .B " mdadm --stop --scan"
917 This will shut down all array that can be shut down (i.e. are not
918 currently in used). This will typically going in a system shutdown script.
920 .B " mdadm --follow --scan --delay=120"
922 If (and only if) there is an Email address or program given in the
923 standard config file, then
924 monitor the status of all arrays listed in that file by
925 polling them ever 2 minutes.
927 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
929 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
932 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
934 .B " mdadm --detail --scan >> mdadm.conf"
936 This will create a prototype config file that describes currently
937 active arrays that are known to be made from partitions of IDE or SCSI drives.
938 This file should be reviewed before being used as it may
939 contain unwanted detail.
941 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
943 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
945 This will find what arrays could be assembled from existign IDE and
946 SCSI whole drives (not partitions) and store the information is the
947 format of a config file.
948 This file is very likely to contain unwanted detail, particularly
951 entries. It should be reviewed and edited before being used as an
954 .B " mdadm --examine --brief --scan --config=partitions"
956 .B " mdadm -Ebsc partitions"
958 Create a list of devices by reading
959 .BR /proc/partitions ,
960 scan these for RAID superblocks, and printout a brief listing of all
963 .B " mdadm -Ac partitions -m 0 /dev/md0"
965 Scan all partitions and devices listed in
969 out of all such devices with a RAID superblock with a minor number of 0.
971 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
973 If config file contains a mail address or alert program, run mdadm in
974 the background in monitor mode monitoring all md devices. Also write
975 pid of mdadm daemon to
978 .B " mdadm --create --help"
980 Providew help about the Create mode.
982 .B " mdadm --config --help"
984 Provide help about the format of the config file.
988 Provide general help.
999 lists all active md devices with information about them.
1001 uses this to find arrays when
1003 is given in Misc mode, and to monitor array reconstruction
1009 The config file lists which devices may be scanned to see if
1010 they contain MD super block, and gives identifying information
1011 (e.g. UUID) about known MD arrays. See
1018 was previously known as
1022 For information on the various levels of
1026 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1027 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1030 for new releases of the RAID driver check out:
1033 .UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1034 ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1039 .UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1040 http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
projects / thirdparty / mdadm.git / blob