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
36 .B MULTIPATH is not a Software RAID mechanism, but does involve
39 each device is a path to one common physical storage device.
43 is a program that can be used to create, manage, and monitor
45 such it provides a similar set of functionality to the
48 The key differences between
55 is a single program and not a collection of programs.
58 can perform (almost) all of its functions without having a
59 configuration file and does not use one by default. Also
61 helps with management of the configuration
65 can provide information about your arrays (through Query, Detail, and Examine)
75 configuration file, at all. It has a different configuration file
76 with a different format and an different purpose.
79 mdadm has 7 major modes of operation:
82 Assemble the parts of a previously created
83 array into an active array. Components can be explicitly given
84 or can be searched for.
86 checks that the components
87 do form a bona fide array, and can, on request, fiddle superblock
88 information so as to assemble a faulty array.
92 Build a legacy array without per-device superblocks.
96 Create a new array with per-device superblocks.
98 '''in several step create-add-add-run or it can all happen with one command.
102 This is for doing things to specific components of an array such as
103 adding new spares and removing faulty devices.
107 This mode allows operations on independent devices such as examine MD
108 superblocks, erasing old superblocks and stopping active arrays.
111 .B "Follow or Monitor"
112 Monitor one or more md devices and act on any state changes. This is
113 only meaningful for raid1, 4, 5, 6 or multipath arrays as
114 only these have interesting state. raid0 or linear never have
115 missing, spare, or failed drives, so there is nothing to monitor.
119 Grow (or shrink) an array, or otherwise reshape it in some way.
120 Currently supported growth options including changing the active size
121 of componenet devices in RAID level 1/4/5/6 and changing the number of
122 active devices in RAID1.
126 Available options are:
129 .BR -A ", " --assemble
130 Assemble a pre-existing array.
134 Build a legacy array without superblocks.
142 Examine a device to see
143 (1) if it is an md device and (2) if it is a component of an md
145 Information about what is discovered is presented.
149 Print detail of one or more md devices.
152 .BR -E ", " --examine
153 Print content of md superblock on device(s).
156 .BR -F ", " --follow ", " --monitor
163 Change the size or shape of an active array.
167 Display help message or, after above option, mode specific help
172 Display more detailed help about command line parsing and some commonly
176 .BR -V ", " --version
177 Print version information for mdadm.
180 .BR -v ", " --verbose
181 Be more verbose about what is happening.
185 Be less verbose. This is used with
192 Be more forceful about certain operations. See the various modes of
193 the exact meaning of this option in different contexts.
196 .BR -c ", " --config=
197 Specify the config file. Default is
198 .BR /etc/mdadm.conf .
199 If the config file given is
201 then nothing will be read, but
203 will act as though the config file contained exactly
204 .B "DEVICE partitions"
207 to find a list of devices to scan.
210 is given for the config file, then
212 will act as though the config file were empty.
218 for missing information.
219 In general, this option gives
221 permission to get any missing information, like component devices,
222 array devices, array identities, and alert destination from the
224 .BR /etc/mdadm.conf .
225 One exception is MISC mode when using
231 says to get a list of array devices from
234 .SH For create or build:
238 Specify chunk size of kibibytes. The default is 64.
242 Specify rounding factor for linear array (==chunk size)
246 Set raid level. When used with
248 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
249 raid5, 5, raid6, 6, multipath, mp. Obviously some of these are synonymous.
253 only linear, raid0, 0, stripe are valid.
256 .BR -p ", " --parity=
257 Set raid5 parity algorithm. Options are:
262 la, ra, ls, rs. The default is left-symmetric.
269 .BR -n ", " --raid-devices=
270 Specify the number of active devices in the array. This, plus the
271 number of spare devices (see below) must equal the number of
273 (including "\fBmissing\fP" devices)
274 that are listed on the command line for
276 Setting a value of 1 is probably
277 a mistake and so requires that
279 be specified first. A value of 1 will then be allowed for linear,
280 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
282 This number can only be changed using
284 for RAID1 arrays, and only on kernels which provide necessary support.
287 .BR -x ", " --spare-devices=
288 Specify the number of spare (eXtra) devices in the initial array.
289 Spares can also be added
290 and removed later. The number of component devices listed
291 on the command line must equal the number of raid devices plus the
292 number of spare devices.
297 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
298 This must be a multiple of the chunk size, and must leave about 128Kb
299 of space at the end of the drive for the RAID superblock.
300 If this is not specified
301 (as it normally is not) the smallest drive (or partition) sets the
302 size, though if there is a variance among the drives of greater than 1%, a warning is
305 This value can be set with
307 for RAID level 1/4/5/6. If the array was created with a size smaller
308 than the currently active drives, the extra space can be accessed
316 that the array pre-existed and is known to be clean. This is only
317 really useful for Building RAID1 array. Only use this if you really
318 know what you are doing. This is currently only supported for --build.
324 run the array, even if some of the components
325 appear to be active in another array or filesystem. Normally
327 will ask for confirmation before including such components in an
328 array. This option causes that question to be suppressed.
334 accept the geometry and layout specified without question. Normally
336 will not allow creation of an array with only one device, and will try
337 to create a raid5 array with one missing drive (as this makes the
338 initial resync work faster). With
341 will not try to be so clever.
344 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
345 Instruct mdadm to create the device file if needed, and to allocate
346 an unused minor number. "yes" or "md" causes a non-partitionable array
347 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
348 later) to be used. The argumentment can also come immediately after
351 For partitionable arrays,
353 will create the device file for the whole array and for the first 4
354 partitions. A different number of partitions can be specified at the
355 end of this option (e.g.
357 If the device name ends with a digit, the partition names add an
358 underscore, a 'p', and a number, e.g. "/dev/home1_p3". If there is no
359 trailing digit, then the partition names just have a number added,
360 e.g. "/dev/scratch3".
366 uuid of array to assemble. Devices which don't have this uuid are
370 .BR -m ", " --super-minor=
371 Minor number of device that array was created for. Devices which
372 don't have this minor number are excluded. If you create an array as
373 /dev/md1, then all superblocks will contain the minor number 1, even if
374 the array is later assembled as /dev/md2.
376 Giving the literal word "dev" for
380 to use the minor number of the md device that is being assembled.
384 will look for super blocks with a minor number of 0.
388 Assemble the array even if some superblocks appear out-of-date
392 Attempt to start the array even if fewer drives were given than are
393 needed for a full array. Normally if not all drives are found and
395 is not used, then the array will be assembled but not started.
398 an attempt will be made to start it anyway.
401 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
402 See this option under Create and Build options.
405 .BR -U ", " --update=
406 Update the superblock on each device while assembling the array. The
407 argument given to this flag can be one of
415 option will adjust the superblock of an array what was created on a Sparc
416 machine running a patched 2.2 Linux kernel. This kernel got the
417 alignment of part of the superblock wrong. You can use the
418 .B "--examine --sparc2.2"
421 to see what effect this would have.
425 option will update the
427 field on each superblock to match the minor number of the array being
428 assembled. This is not needed on 2.6 and later kernels as they make
429 this adjustment automatically.
433 option will correct the summaries in the superblock. That is the
434 counts of total, working, active, failed, and spare devices.
441 hotadd listed devices.
445 remove listed devices. They must not be active. i.e. they should
446 be failed or spare devices.
450 mark listed devices as faulty.
456 .SH For Examine mode:
460 In an array was created on a 2.2 Linux kernel patched with RAID
461 support, the superblock will have been created incorrectly, or at
462 least incompatibly with 2.4 and later kernels. Using the
466 will fix the superblock before displaying it. If this appears to do
467 the right thing, then the array can be successfully assembled using
468 .BR "--assemble --update=sparc2.2" .
474 start a partially built array.
478 deactivate array, releasing all resources.
481 .BR -o ", " --readonly
482 mark array as readonly.
485 .BR -w ", " --readwrite
486 mark array as readwrite.
490 If the device contains a valid md superblock, the block is
491 over-written with zeros. With
493 the block where the superblock would be is over-written even if it
494 doesn't appear to be valid.
502 is set to reflect the status of the device.
504 .SH For Monitor mode:
507 Give a mail address to send alerts to.
510 .BR -p ", " --program ", " --alert
511 Give a program to be run whenever an event is detected.
515 Give a delay in seconds.
517 polls the md arrays and then waits this many seconds before polling
518 again. The default is 60 seconds.
521 .BR -f ", " --daemonise
524 to run as a background daemon if it decides to monitor anything. This
525 causes it to fork and run in the child, and to disconnect form the
526 terminal. The process id of the child is written to stdout.
529 which will only continue monitoring if a mail address or alert program
530 is found in the config file.
533 .BR -1 ", " --oneshot
534 Check arrays only once. This will generate
536 events and more significantly
540 .B " mdadm --monitor --scan -1"
542 from a cron script will ensure regular notification of any degraded arrays.
548 alert for every array found at startup. This alert gets mailed and
549 passed to the alert program. This can be used for testing that alert
550 message to get through successfully.
557 .I md-device options-and-component-devices...
560 .B mdadm --assemble --scan
561 .I md-devices-and-options...
564 .B mdadm --assemble --scan
568 This usage assembles one or more raid arrays from pre-existing components.
569 For each array, mdadm needs to know the md device, the identity of the
570 array, and a number of component-devices. These can be found in a number of ways.
572 In the first usage example (without the
574 the first device given is the md device.
575 In the second usage example, all devices listed are treated as md
576 devices and assembly is attempted.
577 In the third (where no devices are listed) all md devices that are
578 listed in the configuration file are assembled.
580 If precisely one device is listed, but
586 was given and identify information is extracted from the configuration file.
588 The identity can be given with the
592 option, can be found in the config file, or will be taken from the
593 super block on the first component-device listed on the command line.
595 Devices can be given on the
597 command line or in the config file. Only devices which have an md
598 superblock which contains the right identity will be considered for
601 The config file is only used if explicitly named with
603 or requested with (a possibly implicit)
611 is not given, then the config file will only be used to find the
612 identity of md arrays.
614 Normally the array will be started after it is assembled. However if
616 is not given and insufficient drives were listed to start a complete
617 (non-degraded) array, then the array is not started (to guard against
618 usage errors). To insist that the array be started in this case (as
619 may work for RAID1, 4, 5 or 6), give the
625 option is given, either on the command line (--auto) or in the
626 configuration file (e.g. auto=part), then
628 will create the md device if necessary or will re-create it if it
629 doesn't look usable as it is.
631 This can be useful for handling partitioned devices (which don't have
632 a stable device number - it can change after a reboot) and when using
633 "udev" to manage your
635 tree (udev cannot handle md devices because of the unusual device
636 initialisation conventions).
638 If the option to "auto" is "mdp" or "part" or (on the command line
639 only) "p", then mdadm will create a partitionable array, using the
640 first free one that is not inuse, and does not already have an entry
641 in /dev (apart from numeric /dev/md* entries).
643 If the option to "auto" is "yes" or "md" or (on the command line)
644 nothing, then mdadm will create a traditional, non-partitionable md
647 It is expected that the "auto" functionality will be used to create
648 device entries with meaningful names such as "/dev/md/home" or
649 "/dev/md/root", rather than names based on the numerical array number.
651 When using this option to create a partitionable array, the device
652 files for the first 4 partitions are also created. If a different
653 number is required it can be simply appended to the auto option.
654 e.g. "auto=part8". Partition names are created by appending a digit
655 string to the device name, with an intervening "_p" if the device name
660 option is also available in Build and Create modes. As those modes do
661 not use a config file, the "auto=" config option does not apply to
672 .BI --raid-devices= Z
676 This usage is similar to
678 The difference is that it creates a legacy array without a superblock. With
679 these arrays there is no difference between initially creating the array and
680 subsequently assembling the array, except that hopefully there is useful
681 data there in the second case.
683 The level may only be 0, raid0, or linear. All devices must be listed
684 and the array will be started once complete.
695 .BI --raid-devices= Z
699 This usage will initialise a new md array, associate some devices with
700 it, and activate the array.
704 option is given (as described in more detail in the section on
705 Assemble mode), then the md device will be created with a suitable
706 device number if necessary.
708 As devices are added, they are checked to see if they contain raid
709 superblocks or filesystems. They are also checked to see if the variance in
710 device size exceeds 1%.
712 If any discrepancy is found, the array will not automatically be run, though
715 can override this caution.
717 To create a "degraded" array in which some devices are missing, simply
718 give the word "\fBmissing\fP"
719 in place of a device name. This will cause
721 to leave the corresponding slot in the array empty.
722 For a RAID4 or RAID5 array at most one slot can be
723 "\fBmissing\fP"; for a RAID6 array at most two slots.
724 For a RAID1 array, only one real device needs to be given. All of the
728 When creating a RAID5 array,
730 will automatically create a degraded array with an extra spare drive.
731 This is because building the spare into a degraded array is in general faster than resyncing
732 the parity on a non-degraded, but not clean, array. This feature can
733 be over-ridden with the
739 '''option is given, it is not necessary to list any component-devices in this command.
740 '''They can be added later, before a
744 '''is given, the apparent size of the smallest drive given is used.
746 The General Management options that are valid with --create are:
749 insist on running the array even if some devices look like they might
754 start the array readonly - not supported yet.
761 .I options... devices...
764 This usage will allow individual devices in an array to be failed,
765 removed or added. It is possible to perform multiple operations with
766 on command. For example:
768 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
774 and will then remove it from the array and finally add it back
775 in as a spare. However only one md array can be affected by a single
786 MISC mode includes a number if distinct operations that
787 operate on distinct devices. The operations are:
790 The device is examined to see if it is
791 (1) an active md array, or
792 (2) a component of an md array.
793 The information discovered is reported.
797 The device should be an active md device.
799 will display a detailed description of the array.
803 will cause the output to be less detailed and the format to be
804 suitable for inclusion in
805 .BR /etc/mdadm.conf .
808 will normally be 0 unless
810 failed to get useful information about the device(s). However if the
812 option is given, then the exit status will be:
816 The array is functioning normally.
819 The array has at least one failed device.
822 The array has multiple failed devices and hence is unusable (raid4 or
826 There was an error while trying to get information about the device.
831 The device should be a component of an md array.
833 will read the md superblock of the device and display the contents.
838 then multiple devices that are components of the one array
839 are grouped together and reported in a single entry suitable
841 .BR /etc/mdadm.conf .
845 without listing any devices will cause all devices listed in the
846 config file to be examined.
850 The devices should be active md arrays which will be deactivated, as
851 long as they are not currently in use.
855 This will fully activate a partially assembled md array.
859 This will mark an active array as read-only, providing that it is
860 not currently being used.
866 array back to being read/write.
870 For all operations except
873 will cause the operation to be applied to all arrays listed in
878 causes all devices listed in the config file to be examined.
886 .I options... devices...
891 to periodically poll a number of md arrays and to report on any events
894 will never exit once it decides that there are arrays to be checked,
895 so it should normally be run in the background.
897 As well as reporting events,
899 may move a spare drive from one array to another if they are in the
902 and if the destination array has a failed drive but not spares.
904 If any devices are listed on the command line,
906 will only monitor those devices. Otherwise all arrays listed in the
907 configuration file will be monitored. Further, if
909 is given, then any other md devices that appear in
911 will also be monitored.
913 The result of monitoring the arrays is the generation of events.
914 These events are passed to a separate program (if specified) and may
915 be mailed to a given E-mail address.
917 When passing event to program, the program is run once for each event
918 and is given 2 or 3 command-line arguements. The first is the
919 name of the event (see below). The second is the name of the
920 md device which is affected, and the third is the name of a related
921 device if relevant, such as a component device that has failed.
925 is given, then a program or an E-mail address must be specified on the
926 command line or in the config file. If neither are available, then
928 will not monitor anything.
932 will continue monitoring as long as something was found to monitor. If
933 no program or email is given, then each event is reported to
936 The different events are:
941 An md array which previously was configured appears to no longer be
946 An md array started reconstruction.
952 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
953 percentage of the total.
957 An md array that was rebuilding, isn't any more, either because it
958 finished normally or was aborted.
962 An active component device of an array has been marked as faulty.
966 A spare component device which was being rebuilt to replace a faulty
971 A spare component device which was being rebuilt to replace a faulty
972 device as been successfully rebuild and has been made active.
976 A new md array has been detected in the
982 A newly noticed array appears to be degraded. This message is not
985 notices a drive failure which causes degradation, but only when
987 notices that an array is degraded when it first sees the array.
991 A spare drive has been moved from one array in a
993 to another to allow a failed drive to be replaced.
997 An array was found at startup, and the
1008 cause Email to be sent. All events cause the program to be run.
1009 The program is run with two or three arguments, they being the event
1010 name, the array device and possibly a second device.
1012 Each event has an associated array device (e.g.
1014 and possibly a second device. For
1019 the second device is the relevant component device.
1022 the second device is the array that the spare was moved from.
1026 to move spares from one array to another, the different arrays need to
1027 be labelled with the same
1029 in the configuration file. The
1031 name can be any string. It is only necessary that different spare
1032 groups use different names.
1036 detects that an array which is in a spare group has fewer active
1037 devices than necessary for the complete array, and has no spare
1038 devices, it will look for another array in the same spare group that
1039 has a full complement of working drive and a spare. It will then
1040 attempt to remove the spare from the second drive and add it to the
1042 If the removal succeeds but the adding fails, then it is added back to
1046 The GROW mode is used for changing the size or shape of an active
1048 For this to work, the kernel must support the necessary change.
1049 Various types of growth may be added during 2.6 development, possibly
1050 including restructuring a raid5 array to have more active devices.
1052 Currently the only support available is to change the "size" attribute
1053 for arrays with redundancy, and the raid-disks attribute of RAID1
1056 Normally when an array is build the "size" it taken from the smallest
1057 of the drives. If all the small drives in an arrays are, one at a
1058 time, removed and replaced with larger drives, then you could have an
1059 array of large drives with only a small amount used. In this
1060 situation, changing the "size" with "GROW" mode will allow the extra
1061 space to start being used. If the size is increased in this way, a
1062 "resync" process will start to make sure the new parts of the array
1065 Note that when an array changes size, any filesystem that may be
1066 stored in the array will not automatically grow to use the space. The
1067 filesystem will need to be explicitly told to use the extra space.
1069 A RAID1 array can work with any number of devices from 1 upwards
1070 (though 1 is not very useful). There may be times which you want to
1071 increase or decrease the number of active devices. Note that this is
1072 different to hot-add or hot-remove which changes the number of
1075 When reducing the number of devices in a RAID1 array, the slots which
1076 are to be removed from the array must already be vacant. That is, the
1077 devices that which were in those slots must be failed and removed.
1079 When the number of devices is increased, any hot spares that are
1080 present may be activated immediately.
1084 .B " mdadm --query /dev/name-of-device"
1086 This will find out if a given device is a raid array, or is part of
1087 one, and will provide brief information about the device.
1089 .B " mdadm --assemble --scan"
1091 This will assemble and start all arrays listed in the standard confile
1092 file. This command will typically go in a system startup file.
1094 .B " mdadm --stop --scan"
1096 This will shut down all array that can be shut down (i.e. are not
1097 currently in used). This will typically going in a system shutdown script.
1099 .B " mdadm --follow --scan --delay=120"
1101 If (and only if) there is an Email address or program given in the
1102 standard config file, then
1103 monitor the status of all arrays listed in that file by
1104 polling them ever 2 minutes.
1106 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1108 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1111 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1113 .B " mdadm --detail --scan >> mdadm.conf"
1115 This will create a prototype config file that describes currently
1116 active arrays that are known to be made from partitions of IDE or SCSI drives.
1117 This file should be reviewed before being used as it may
1118 contain unwanted detail.
1120 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1122 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1124 This will find what arrays could be assembled from existign IDE and
1125 SCSI whole drives (not partitions) and store the information is the
1126 format of a config file.
1127 This file is very likely to contain unwanted detail, particularly
1130 entries. It should be reviewed and edited before being used as an
1133 .B " mdadm --examine --brief --scan --config=partitions"
1135 .B " mdadm -Ebsc partitions"
1137 Create a list of devices by reading
1138 .BR /proc/partitions ,
1139 scan these for RAID superblocks, and printout a brief listing of all
1142 .B " mdadm -Ac partitions -m 0 /dev/md0"
1144 Scan all partitions and devices listed in
1145 .BR /proc/partitions
1148 out of all such devices with a RAID superblock with a minor number of 0.
1150 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1152 If config file contains a mail address or alert program, run mdadm in
1153 the background in monitor mode monitoring all md devices. Also write
1154 pid of mdadm daemon to
1155 .BR /var/run/mdadm .
1157 .B " mdadm --create --help"
1159 Providew help about the Create mode.
1161 .B " mdadm --config --help"
1163 Provide help about the format of the config file.
1167 Provide general help.
1178 lists all active md devices with information about them.
1180 uses this to find arrays when
1182 is given in Misc mode, and to monitor array reconstruction
1188 The config file lists which devices may be scanned to see if
1189 they contain MD super block, and gives identifying information
1190 (e.g. UUID) about known MD arrays. See
1197 was previously known as
1201 For information on the various levels of
1205 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1206 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1209 for new releases of the RAID driver check out:
1212 .UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1213 ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1218 .UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1219 http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
projects / thirdparty / mdadm.git / blob