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 either
338 option will adjust the superblock of an array what was created on a Sparc
339 machine running a patched 2.2 Linux kernel. This kernel got the
340 alignment of part of the superblock wrong. You can use the
341 .B "--examine --sparc2.2"
344 to see what effect this would have.
348 option will update the
350 field on each superblock to match the minor number of the array being
351 assembled. This is not need on 2.6 and later kernels as they make
352 this adjustment automatically.
360 hotadd listed devices.
364 remove listed devices. They must not be active. i.e. they should
365 be failed or spare devices.
369 mark listed devices as faulty.
375 .SH For Examine mode:
379 In an array was created on a 2.2 Linux kernel patched with RAID
380 support, the superblock will have been created incorrectly, or at
381 least incompatibly with 2.4 and later kernels. Using the
385 will fix the superblock before displaying it. If this appears to do
386 the right thing, then the array can be successfully assembled using
387 .BR "--assemble --update=sparc2.2" .
393 start a partially built array.
397 deactivate array, releasing all resources.
400 .BR -o ", " --readonly
401 mark array as readonly.
404 .BR -w ", " --readwrite
405 mark array as readwrite.
409 If the device contains a valid md superblock, the block is
410 over-written with zeros. With
412 the block where the superblock would be is over-written even if it
413 doesn't appear to be valid.
415 .SH For Monitor mode:
418 Give a mail address to send alerts to.
421 .BR -p ", " --program ", " --alert
422 Give a program to be run whenever an event is detected.
426 Give a delay in seconds.
428 polls the md arrays and then waits this many seconds before polling
429 again. The default is 60 seconds.
432 .BR -f ", " --daemonise
435 to run as a background daemon if it decides to monitor anything. This
436 causes it to fork and run in the child, and to disconnect form the
437 terminal. The process id of the child is written to stdout.
440 which will only continue monitoring if a mail address or alert program
441 is found in the config file.
444 .BR -1 ", " --oneshot
445 Check arrays only once. This will generate
447 events and more significantly
451 .B " mdadm --monitor --scan -1"
453 from a cron script will ensure regular notification of any degraded arrays.
460 .I md-device options-and-component-devices...
463 .B mdadm --assemble --scan
464 .I md-devices-and-options...
467 .B mdadm --assemble --scan
471 This usage assembles one or more raid arrays from pre-existing components.
472 For each array, mdadm needs to know the md device, the identity of the
473 array, and a number of component-devices. These can be found in a number of ways.
475 In the first usage example (without the
477 the first device given is the md device.
478 In the second usage example, all devices listed are treated as md
479 devices and assembly is attempted.
480 In the third (where no devices are listed) all md devices that are
481 listed in the configuration file are assembled.
483 If precisely one device is listed, but
489 was given and identify information is extracted from the configuration file.
491 The identity can be given with the
495 option, can be found in the config file, or will be taken from the
496 super block on the first component-device listed on the command line.
498 Devices can be given on the
500 command line or in the config file. Only devices which have an md
501 superblock which contains the right identity will be considered for
504 The config file is only used if explicitly named with
506 or requested with (a possibly implicit)
514 is not given, then the config file will only be used to find the
515 identity of md arrays.
517 Normally the array will be started after it is assembled. However if
519 is not given and insufficient drives were listed to start a complete
520 (non-degraded) array, then the array is not started (to guard against
521 usage errors). To insist that the array be started in this case (as
522 may work for RAID1 or RAID5), give the
535 .BI --raid-devices= Z
539 This usage is similar to
541 The difference is that it creates a legacy array without a superblock. With
542 these arrays there is no difference between initially creating the array and
543 subsequently assembling the array, except that hopefully there is useful
544 data there in the second case.
546 The level may only be 0, raid0, or linear. All devices must be listed
547 and the array will be started once complete.
558 .BI --raid-devices= Z
562 This usage will initialise a new md array, associate some devices with
563 it, and activate the array.
565 As devices are added, they are checked to see if they contain raid
566 superblocks or filesystems. They are also checked to see if the variance in
567 device size exceeds 1%.
569 If any discrepancy is found, the array will not automatically be run, though
572 can override this caution.
574 To create a "degraded" array in which some devices are missing, simply
575 give the word "\fBmissing\fP"
576 in place of a device name. This will cause
578 to leave the corresponding slot in the array empty.
579 For a RAID4 or RAID5 array at most one slot can be
581 For a RAID1 array, only one real device needs to be given. All of the
587 '''option is given, it is not necessary to list any component-devices in this command.
588 '''They can be added later, before a
592 '''is given, the apparent size of the smallest drive given is used.
594 The General Management options that are valid with --create are:
597 insist of running the array even if some devices look like they might
602 start the array readonly - not supported yet.
609 .I options... devices...
612 This usage will allow individual devices in an array to be failed,
613 removed or added. It is possible to perform multiple operations with
614 on command. For example:
616 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
622 and will then remove it from the array and finally add it back
623 in as a spare. However only one md array can be affected by a single
634 MISC mode includes a number if distinct operations that
635 operate on distinct devices. The operations are:
638 The device is examined to see if it is
639 (1) an active md array, or
640 (2) a component of an md array.
641 The information discovered is reported.
645 The device should be an active md device.
647 will display a detailed description of the array.
651 will cause the output to be less detailed and the format to be
652 suitable for inclusion in
653 .BR /etc/mdadm.conf .
657 The device should be a component of an md array.
659 will read the md superblock of the device and display the contents.
664 then multiple devices that are components of the one array
665 are grouped together and reported in a single entry suitable
667 .BR /etc/mdadm.conf .
671 without listing any devices will cause all devices listed in the
672 config file to be examined.
676 This devices should active md arrays which will be deactivated, if
677 they are not currently in use.
681 This will fully activate a partially assembled md array.
685 This will mark an active array as read-only, providing that it is
686 not currently being used.
692 array back to being read/write.
696 For all operations except
699 will cause the operation to be applied to all arrays listed in
704 causes all devices listed in the config file to be examined.
712 .I options... devices...
717 to periodically poll a number of md arrays and to report on any events
720 will never exit once it decides that there are arrays to be checked,
721 so it should normally be run in the background.
723 As well as reporting events,
725 may move a spare drive from one array to another if they are in the
728 and if the destination array has a failed drive but not spares.
730 If any devices are listed on the command line,
732 will only monitor those devices. Otherwise all arrays listed in the
733 configuration file will be monitored. Further, if
735 is given, then any other md devices that appear in
737 will also be monitored.
739 The result of monitoring the arrays is the generation of events.
740 These events are passed to a separate program (if specified) and may
741 be mailed to a given E-mail address.
743 When passing event to program, the program is run once for each event
744 and is given 2 or 3 command-line arguements. The first is the
745 name of the event (see below). The second is the name of the
746 md device which is affected, and the third is the name of a related
747 device if relevant, such as a component device that has failed.
751 is given, then a program or an E-mail address must be specified on the
752 command line or in the config file. If neither are available, then
754 will not monitor anything.
758 will continue monitoring as long as something was found to monitor. If
759 no program or email is given, then each event is reported to
762 The different events are:
767 An md array which previously was configured appears to no longer be
772 An md array started reconstruction.
778 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
779 percentage of the total.
783 An active component device of an array has been marked as faulty.
787 A spare component device which was being rebuilt to replace a faulty
792 A spare component device which was being rebuilt to replace a faulty
793 device as been successfully rebuild and has been made active.
797 A new md array has been detected in the
803 A newly noticed array appears to be degraded. This message is not
806 notices a drive failure which causes degradation, but only when
808 notices that an array is degraded when it first sees the array.
812 A spare drive has been moved from one array in a
814 to another to allow a failed drive to be replaced.
822 cause Email to be sent. All events cause the program to be run.
823 The program is run with two or three arguments, they being the event
824 name, the array device and possibly a second device.
826 Each event has an associated array device (e.g.
828 and possibly a second device. For
833 the second device is the relevant component device.
836 the second device is the array that the spare was moved from.
840 to move spares from one array to another, the different arrays need to
841 be labelled with the same
843 in the configuration file. The
845 name can be any string. It is only necessary that different spare
846 groups use different names.
850 detects that an array which is in a spare group has fewer active
851 devices than necessary for the complete array, and has no spare
852 devices, it will look for another array in the same spare group that
853 has a full complement of working drive and a spare. It will then
854 attempt to remove the spare from the second drive and add it to the
856 If the removal succeeds but the adding fails, then it is added back to
861 .B " mdadm --query /dev/name-of-device"
863 This will find out if a given device is a raid array, or is part of
864 one, and will provide brief information about the device.
866 .B " mdadm --assemble --scan"
868 This will assemble and start all arrays listed in the standard confile
869 file. This command will typically go in a system startup file.
871 .B " mdadm --stop --scan"
873 This will shut down all array that can be shut down (i.e. are not
874 currently in used). This will typically going in a system shutdown script.
876 .B " mdadm --follow --scan --delay=120"
878 If (and only if) there is an Email address or program given in the
879 standard config file, then
880 monitor the status of all arrays listed in that file by
881 polling them ever 2 minutes.
883 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
885 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
888 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
890 .B " mdadm --detail --scan >> mdadm.conf"
892 This will create a prototype config file that describes currently
893 active arrays that are known to be made from partitions of IDE or SCSI drives.
894 This file should be reviewed before being used as it may
895 contain unwanted detail.
897 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
899 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
901 This will find what arrays could be assembled from existign IDE and
902 SCSI whole drives (not partitions) and store the information is the
903 format of a config file.
904 This file is very likely to contain unwanted detail, particularly
907 entries. It should be reviewed and edited before being used as an
910 .B " mdadm --examine --brief --scan --config=partitions"
912 .B " mdadm -Ebsc partitions"
914 Create a list of devices by reading
915 .BR /proc/partitions ,
916 scan these for RAID superblocks, and printout a brief listing of all
919 .B " mdadm -Ac partitions -m 0 /dev/md0"
921 Scan all partitions and devices listed in
925 out of all such devices with a RAID superblock with a minor number of 0.
927 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
929 If config file contains a mail address or alert program, run mdadm in
930 the background in monitor mode monitoring all md devices. Also write
931 pid of mdadm daemon to
934 .B " mdadm --create --help"
936 Providew help about the Create mode.
938 .B " mdadm --config --help"
940 Provide help about the format of the config file.
944 Provide general help.
955 lists all active md devices with information about them.
957 uses this to find arrays when
959 is given in Misc mode, and to monitor array reconstruction
965 The config file lists which devices may be scanned to see if
966 they contain MD super block, and gives identifying information
967 (e.g. UUID) about known MD arrays. See
974 was previously known as
978 For information on the various levels of
982 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
983 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
986 for new releases of the RAID driver check out:
989 .UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
990 ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
995 .UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
996 http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
projects / thirdparty / mdadm.git / blob