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
39 is not a Software RAID mechanism, but does involve
42 each device is a path to one common physical storage device.
45 is also not true RAID, and it only involves one device. It
46 provides a layer over a true device that can be used to inject faults.
49 '''is a program that can be used to create, manage, and monitor
51 '''such it provides a similar set of functionality to the
54 '''The key differences between
61 '''is a single program and not a collection of programs.
64 '''can perform (almost) all of its functions without having a
65 '''configuration file and does not use one by default. Also
67 '''helps with management of the configuration
71 '''can provide information about your arrays (through Query, Detail, and Examine)
81 '''configuration file, at all. It has a different configuration file
82 '''with a different format and an different purpose.
85 mdadm has 7 major modes of operation:
88 Assemble the parts of a previously created
89 array into an active array. Components can be explicitly given
90 or can be searched for.
92 checks that the components
93 do form a bona fide array, and can, on request, fiddle superblock
94 information so as to assemble a faulty array.
98 Build an array that doesn't have per-device superblocks. For these
101 cannot differentiate between initial creation and subsequent assembly
102 of an array. It also cannot perform any checks that appropriate
103 devices have been requested. Because of this, the
105 mode should only be used together with a complete understanding of
110 Create a new array with per-device superblocks.
112 '''in several step create-add-add-run or it can all happen with one command.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for raid1, 4, 5, 6, 10 or multipath arrays as
118 only these have interesting state. raid0 or linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices in RAID level 1/4/5/6 and changing the number of
126 active devices in RAID1.
130 This is for doing things to specific components of an array such as
131 adding new spares and removing faulty devices.
135 This is an 'everything else' mode that supports operations on active
136 arrays, operations on component devices such as erasing old superblocks, and
137 information gathering operations.
138 '''This mode allows operations on independent devices such as examine MD
139 '''superblocks, erasing old superblocks and stopping active arrays.
143 .SH Options for selecting a mode are:
146 .BR -A ", " --assemble
147 Assemble a pre-existing array.
151 Build a legacy array without superblocks.
158 .BR -F ", " --follow ", " --monitor
165 Change the size or shape of an active array.
167 If a device is given before any options, or if the first option is
172 then the MANAGE mode is assume.
173 Anything other than these will cause the
177 .SH Options that are not mode-specific are:
181 Display general help message or, after one of the above options, a
182 mode specific help message.
186 Display more detailed help about command line parsing and some commonly
190 .BR -V ", " --version
191 Print version information for mdadm.
194 .BR -v ", " --verbose
195 Be more verbose about what is happening. This can be used twice to be
197 The extra verbosity currently only affects
200 .BR "--examine --scan" .
204 Avoid printing purely informative messages. With this,
206 will be silent unless there is something really important to report.
210 Be less verbose. This is used with
218 gives an intermediate level of verbosity.
222 Be more forceful about certain operations. See the various modes of
223 the exact meaning of this option in different contexts.
226 .BR -c ", " --config=
227 Specify the config file. Default is to use
228 .BR /etc/mdadm.conf ,
229 or if that is missing, then
230 .BR /etc/mdadm/mdadm.conf .
231 If the config file given is
233 then nothing will be read, but
235 will act as though the config file contained exactly
236 .B "DEVICE partitions"
239 to find a list of devices to scan.
242 is given for the config file, then
244 will act as though the config file were empty.
250 for missing information.
251 In general, this option gives
253 permission to get any missing information, like component devices,
254 array devices, array identities, and alert destination from the
256 .BR /etc/mdadm.conf .
257 One exception is MISC mode when using
263 says to get a list of array devices from
267 .B -e ", " --metadata=
268 Declare the style of superblock (raid metadata) to be used. The
269 default is 0.90 for --create, and to guess for other operations.
273 .IP "0, 0.90, default"
274 Use the original 0.90 format superblock. This format limits arrays to
275 28 componenet devices and limits component devices of levels 1 and
276 greater to 2 terabytes.
277 .IP "1, 1.0, 1.1, 1.2"
278 Use the new version-1 format superblock. This has few restrictions.
279 The different subversion store the superblock at different locations
280 on the device, either at the end (for 1.0), at the start (for 1.1) or
281 4K from the start (for 1.2).
284 .SH For create, build, or grow:
287 .BR -n ", " --raid-devices=
288 Specify the number of active devices in the array. This, plus the
289 number of spare devices (see below) must equal the number of
291 (including "\fBmissing\fP" devices)
292 that are listed on the command line for
294 Setting a value of 1 is probably
295 a mistake and so requires that
297 be specified first. A value of 1 will then be allowed for linear,
298 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
300 This number can only be changed using
302 for RAID1 arrays, and only on kernels which provide necessary support.
305 .BR -x ", " --spare-devices=
306 Specify the number of spare (eXtra) devices in the initial array.
307 Spares can also be added
308 and removed later. The number of component devices listed
309 on the command line must equal the number of raid devices plus the
310 number of spare devices.
315 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
316 This must be a multiple of the chunk size, and must leave about 128Kb
317 of space at the end of the drive for the RAID superblock.
318 If this is not specified
319 (as it normally is not) the smallest drive (or partition) sets the
320 size, though if there is a variance among the drives of greater than 1%, a warning is
323 This value can be set with
325 for RAID level 1/4/5/6. If the array was created with a size smaller
326 than the currently active drives, the extra space can be accessed
329 The size can be given as
331 which means to choose the largest size that fits on all current drives.
335 Specify chunk size of kibibytes. The default is 64.
339 Specify rounding factor for linear array (==chunk size)
343 Set raid level. When used with
345 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
346 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty. Obviously some of these are synonymous.
350 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
352 Not yet supported with
356 .BR -p ", " --layout=
357 This option configures the fine details of data layout for raid5,
358 and raid10 arrays, and controls the failure modes for
361 The layout of the raid5 parity block can be one of
366 la, ra, ls, rs. The default is left-symmetric.
368 When setting the failure mode for
386 Each mode can be followed by a number which is used as a period
387 between fault generation. Without a number, the fault is generated
388 once on the first relevant request. With a number, the fault will be
389 generated after that many request, and will continue to be generated
390 every time the period elapses.
392 Multiple failure modes can be current simultaneously by using the
393 "--grow" option to set subsequent failure modes.
395 "clear" or "none" will remove any pending or periodic failure modes,
396 and "flush" will clear any persistent faults.
398 To set the parity with "--grow", the level of the array ("faulty")
399 must be specified before the fault mode is specified.
401 Finally, the layout options for RAID10 are either 'n' or 'p' followed
402 by a small number. The default is 'n2'.
405 signals 'near' copies (multiple copies of one data block are at
406 similar offsets in different devices) while
409 (multiple copies have very different offsets). See md(4) for more
410 detail about 'near' and 'far'.
412 The number is the number of copies of each datablock. 2 is normal, 3
413 can be useful. This number can be at most equal to the number of
414 devices in the array. It does not need to divide evenly into that
415 number (e.g. it is perfectly legal to have an 'n2' layout for an array
416 with an odd number of devices).
420 same as --layout (thus explaining the p of
424 .BR -b ", " --bitmap=
425 Specify a file to store a write-intent bitmap in. The file should not
426 exist unless --force is also given. The same file should be provided
427 when assembling the array. If the word
429 is given, then the bitmap is stored with the metadata on the array,
430 and so is replicated on all devices. If the word
434 mode, then any bitmap that is present is removed.
436 To help catch typing errors, the filename must contain at least one
437 slash ('/') if it is a real file (not 'internal' or 'none').
439 Note: external bitmaps are only known to work on ext2 and ext3.
440 Storing bitmap files on other filesystems may result in serious problems.
445 Set the chunksize of the bitmap. Each bit corresponds to that many
446 Kilobytes of storage. Default is 4 when using a file based bitmap.
449 bitmap, the chunksize is automatically determined to make best use of
454 .BR -W ", " --write-mostly
455 subsequent devices lists in a
460 command will be flagged as 'write-mostly'. This is valid for RAID1
461 only and means that the 'md' driver will avoid reading from these
462 devices if at all possible. This can be useful if mirroring over a
467 Specify that write-behind mode should be enabled (valid for RAID1
468 only). If an argument is specified, it will set the maximum number
469 of outstanding writes allowed. The default value is 256.
470 A write-intent bitmap is required in order to use write-behind
471 mode, and write-behind is only attempted on drives marked as
478 that the array pre-existed and is known to be clean. It can be useful
479 when trying to recover from a major failure as you can be sure that no
480 data will be affected unless you actually write to the array. It can
481 also be used when creating a RAID1 or RAID10 if you want to avoid the
482 initial resync, however this practice - while normally safe - is not
483 recommended. Use this ony if you really know what you are doing.
487 This is needed when --grow is used to increase the number of
488 raid-devices in a RAID5 if there are no spare devices available.
489 See the section below on RAID_DEVICE CHANGES. The file should be
490 stored on a separate device, not on the raid array being reshaped.
496 for the array. This is currently only effective when creating an
497 array with a version-1 superblock. The name is a simple textual
498 string that can be used to identify array components when assembling.
504 run the array, even if some of the components
505 appear to be active in another array or filesystem. Normally
507 will ask for confirmation before including such components in an
508 array. This option causes that question to be suppressed.
514 accept the geometry and layout specified without question. Normally
516 will not allow creation of an array with only one device, and will try
517 to create a raid5 array with one missing drive (as this makes the
518 initial resync work faster). With
521 will not try to be so clever.
524 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
525 Instruct mdadm to create the device file if needed, possibly allocating
526 an unused minor number. "md" causes a non-partitionable array
527 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
528 later) to be used. "yes" requires the named md device to have
529 a 'standard' format, and the type and minor number will be determined
530 from this. See DEVICE NAMES below.
532 The argument can also come immediately after
537 is also given, then any
539 entries in the config file will over-ride the
541 instruction given on the command line.
543 For partitionable arrays,
545 will create the device file for the whole array and for the first 4
546 partitions. A different number of partitions can be specified at the
547 end of this option (e.g.
549 If the device name ends with a digit, the partition names add a 'p',
550 and a number, e.g. "/dev/home1p3". If there is no
551 trailing digit, then the partition names just have a number added,
552 e.g. "/dev/scratch3".
554 If the md device name is in a 'standard' format as described in DEVICE
555 NAMES, then it will be created, if necessary, with the appropriate
556 number based on that name. If the device name is not in one of these
557 formats, then a unused minor number will be allocated. The minor
558 number will be considered unused if there is no active array for that
559 number, and there is no entry in /dev for that number and with a
566 uuid of array to assemble. Devices which don't have this uuid are
570 .BR -m ", " --super-minor=
571 Minor number of device that array was created for. Devices which
572 don't have this minor number are excluded. If you create an array as
573 /dev/md1, then all superblocks will contain the minor number 1, even if
574 the array is later assembled as /dev/md2.
576 Giving the literal word "dev" for
580 to use the minor number of the md device that is being assembled.
584 will look for super blocks with a minor number of 0.
588 Specify the name of the array to assemble. This must be the name
589 that was specified when creating the array.
593 Assemble the array even if some superblocks appear out-of-date
597 Attempt to start the array even if fewer drives were given than are
598 needed for a full array. Normally if not all drives are found and
600 is not used, then the array will be assembled but not started.
603 an attempt will be made to start it anyway.
606 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
607 See this option under Create and Build options.
610 .BR -b ", " --bitmap=
611 Specify the bitmap file that was given when the array was created. If
614 bitmap, there is no need to specify this when assembling the array.
620 was used to grow the number of raid-devices in a RAID5, and the system
621 crashed during the critical section, then the same
623 must be presented to --assemble to allow possibly corrupted data to be
627 .BR -U ", " --update=
628 Update the superblock on each device while assembling the array. The
629 argument given to this flag can be one of
640 option will adjust the superblock of an array what was created on a Sparc
641 machine running a patched 2.2 Linux kernel. This kernel got the
642 alignment of part of the superblock wrong. You can use the
643 .B "--examine --sparc2.2"
646 to see what effect this would have.
650 option will update the
652 field on each superblock to match the minor number of the array being
653 assembled. This is not needed on 2.6 and later kernels as they make
654 this adjustment automatically.
658 option will change the uuid of the array. If a UUID is given with the
659 "--uuid" option that UUID will be used as a new UUID and with
661 be used to help identify the devices in the array.
662 If no "--uuid" is given, a random uuid is chosen.
666 option will cause the array to be marked
668 meaning that any redundancy in the array (e.g. parity for raid5,
669 copies for raid1) may be incorrect. This will cause the raid system
670 to perform a "resync" pass to make sure that all redundant information
675 option allows arrays to be moved between machines with different
677 When assembling such an array for the first time after a move, giving
678 .B "--update=byteorder"
681 to expect superblocks to have their byteorder reversed, and will
682 correct that order before assembling the array. This is only valid
683 with original (Version 0.90) superblocks.
687 option will correct the summaries in the superblock. That is the
688 counts of total, working, active, failed, and spare devices.
694 hot-add listed devices.
698 re-add a device that was recently removed from an array.
702 remove listed devices. They must not be active. i.e. they should
703 be failed or spare devices.
707 mark listed devices as faulty.
714 Each of these options require that the first device list is the array
715 to be acted upon and the remainder are component devices to be added,
716 removed, or marked as fault. Several different operations can be
717 specified for different devices, e.g.
719 mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
721 Each operation applies to all devices listed until the next
724 If an array is using a write-intent bitmap, then devices which have
725 been removed can be re-added in a way that avoids a full
726 reconstruction but instead just updated the blocks that have changed
727 since the device was removed. For arrays with persistent metadata
728 (superblocks) this is done automatically. For arrays created with
730 mdadm needs to be told that this device we removed recently with
733 Devices can only be removed from an array if they are not in active
734 use. i.e. that must be spares or failed devices. To remove an active
735 device, it must be marked as
743 Examine a device to see
744 (1) if it is an md device and (2) if it is a component of an md
746 Information about what is discovered is presented.
750 Print detail of one or more md devices.
753 .BR -E ", " --examine
754 Print content of md superblock on device(s).
757 If an array was created on a 2.2 Linux kernel patched with RAID
758 support, the superblock will have been created incorrectly, or at
759 least incompatibly with 2.4 and later kernels. Using the
763 will fix the superblock before displaying it. If this appears to do
764 the right thing, then the array can be successfully assembled using
765 .BR "--assemble --update=sparc2.2" .
768 .BR -X ", " --examine-bitmap
769 Report information about a bitmap file.
773 start a partially built array.
777 deactivate array, releasing all resources.
780 .BR -o ", " --readonly
781 mark array as readonly.
784 .BR -w ", " --readwrite
785 mark array as readwrite.
789 If the device contains a valid md superblock, the block is
790 over-written with zeros. With
792 the block where the superblock would be is over-written even if it
793 doesn't appear to be valid.
801 is set to reflect the status of the device.
803 .SH For Monitor mode:
806 Give a mail address to send alerts to.
809 .BR -p ", " --program ", " --alert
810 Give a program to be run whenever an event is detected.
814 Cause all events to be reported through 'syslog'. The messages have
815 facility of 'daemon' and varying priorities.
819 Give a delay in seconds.
821 polls the md arrays and then waits this many seconds before polling
822 again. The default is 60 seconds.
825 .BR -f ", " --daemonise
828 to run as a background daemon if it decides to monitor anything. This
829 causes it to fork and run in the child, and to disconnect form the
830 terminal. The process id of the child is written to stdout.
833 which will only continue monitoring if a mail address or alert program
834 is found in the config file.
837 .BR -i ", " --pid-file
840 is running in daemon mode, write the pid of the daemon process to
841 the specified file, instead of printing it on standard output.
844 .BR -1 ", " --oneshot
845 Check arrays only once. This will generate
847 events and more significantly
853 .B " mdadm --monitor --scan -1"
855 from a cron script will ensure regular notification of any degraded arrays.
861 alert for every array found at startup. This alert gets mailed and
862 passed to the alert program. This can be used for testing that alert
863 message do get through successfully.
870 .I md-device options-and-component-devices...
873 .B mdadm --assemble --scan
874 .I md-devices-and-options...
877 .B mdadm --assemble --scan
881 This usage assembles one or more raid arrays from pre-existing components.
882 For each array, mdadm needs to know the md device, the identity of the
883 array, and a number of component-devices. These can be found in a number of ways.
885 In the first usage example (without the
887 the first device given is the md device.
888 In the second usage example, all devices listed are treated as md
889 devices and assembly is attempted.
890 In the third (where no devices are listed) all md devices that are
891 listed in the configuration file are assembled.
893 If precisely one device is listed, but
899 was given and identify information is extracted from the configuration file.
901 The identity can be given with the
905 option, can be found in the config file, or will be taken from the
906 super block on the first component-device listed on the command line.
908 Devices can be given on the
910 command line or in the config file. Only devices which have an md
911 superblock which contains the right identity will be considered for
914 The config file is only used if explicitly named with
916 or requested with (a possibly implicit)
924 is not given, then the config file will only be used to find the
925 identity of md arrays.
927 Normally the array will be started after it is assembled. However if
929 is not given and insufficient drives were listed to start a complete
930 (non-degraded) array, then the array is not started (to guard against
931 usage errors). To insist that the array be started in this case (as
932 may work for RAID1, 4, 5, 6, or 10), give the
938 option is given, either on the command line (--auto) or in the
939 configuration file (e.g. auto=part), then
941 will create the md device if necessary or will re-create it if it
942 doesn't look usable as it is.
944 This can be useful for handling partitioned devices (which don't have
945 a stable device number - it can change after a reboot) and when using
946 "udev" to manage your
948 tree (udev cannot handle md devices because of the unusual device
949 initialisation conventions).
951 If the option to "auto" is "mdp" or "part" or (on the command line
952 only) "p", then mdadm will create a partitionable array, using the
953 first free one that is not in use, and does not already have an entry
954 in /dev (apart from numeric /dev/md* entries).
956 If the option to "auto" is "yes" or "md" or (on the command line)
957 nothing, then mdadm will create a traditional, non-partitionable md
960 It is expected that the "auto" functionality will be used to create
961 device entries with meaningful names such as "/dev/md/home" or
962 "/dev/md/root", rather than names based on the numerical array number.
964 When using this option to create a partitionable array, the device
965 files for the first 4 partitions are also created. If a different
966 number is required it can be simply appended to the auto option.
967 e.g. "auto=part8". Partition names are created by appending a digit
968 string to the device name, with an intervening "p" if the device name
973 option is also available in Build and Create modes. As those modes do
974 not use a config file, the "auto=" config option does not apply to
985 .BI --raid-devices= Z
989 This usage is similar to
991 The difference is that it creates an array without a superblock. With
992 these arrays there is no difference between initially creating the array and
993 subsequently assembling the array, except that hopefully there is useful
994 data there in the second case.
996 The level may raid0, linear, multipath, or faulty, or one of their
997 synonyms. All devices must be listed and the array will be started
1009 .BI --raid-devices= Z
1013 This usage will initialise a new md array, associate some devices with
1014 it, and activate the array.
1018 option is given (as described in more detail in the section on
1019 Assemble mode), then the md device will be created with a suitable
1020 device number if necessary.
1022 As devices are added, they are checked to see if they contain raid
1023 superblocks or filesystems. They are also checked to see if the variance in
1024 device size exceeds 1%.
1026 If any discrepancy is found, the array will not automatically be run, though
1029 can override this caution.
1031 To create a "degraded" array in which some devices are missing, simply
1032 give the word "\fBmissing\fP"
1033 in place of a device name. This will cause
1035 to leave the corresponding slot in the array empty.
1036 For a RAID4 or RAID5 array at most one slot can be
1037 "\fBmissing\fP"; for a RAID6 array at most two slots.
1038 For a RAID1 array, only one real device needs to be given. All of the
1042 When creating a RAID5 array,
1044 will automatically create a degraded array with an extra spare drive.
1045 This is because building the spare into a degraded array is in general faster than resyncing
1046 the parity on a non-degraded, but not clean, array. This feature can
1047 be over-ridden with the
1053 '''option is given, it is not necessary to list any component-devices in this command.
1054 '''They can be added later, before a
1058 '''is given, the apparent size of the smallest drive given is used.
1060 The General Management options that are valid with --create are:
1063 insist on running the array even if some devices look like they might
1068 start the array readonly - not supported yet.
1076 .I options... devices...
1079 This usage will allow individual devices in an array to be failed,
1080 removed or added. It is possible to perform multiple operations with
1081 on command. For example:
1083 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1089 and will then remove it from the array and finally add it back
1090 in as a spare. However only one md array can be affected by a single
1101 MISC mode includes a number of distinct operations that
1102 operate on distinct devices. The operations are:
1105 The device is examined to see if it is
1106 (1) an active md array, or
1107 (2) a component of an md array.
1108 The information discovered is reported.
1112 The device should be an active md device.
1114 will display a detailed description of the array.
1118 will cause the output to be less detailed and the format to be
1119 suitable for inclusion in
1120 .BR /etc/mdadm.conf .
1123 will normally be 0 unless
1125 failed to get useful information about the device(s). However if the
1127 option is given, then the exit status will be:
1131 The array is functioning normally.
1134 The array has at least one failed device.
1137 The array has multiple failed devices and hence is unusable (raid4 or
1141 There was an error while trying to get information about the device.
1146 The device should be a component of an md array.
1148 will read the md superblock of the device and display the contents.
1153 then multiple devices that are components of the one array
1154 are grouped together and reported in a single entry suitable
1156 .BR /etc/mdadm.conf .
1160 without listing any devices will cause all devices listed in the
1161 config file to be examined.
1165 The devices should be active md arrays which will be deactivated, as
1166 long as they are not currently in use.
1170 This will fully activate a partially assembled md array.
1174 This will mark an active array as read-only, providing that it is
1175 not currently being used.
1181 array back to being read/write.
1185 For all operations except
1188 will cause the operation to be applied to all arrays listed in
1193 causes all devices listed in the config file to be examined.
1201 .I options... devices...
1206 to periodically poll a number of md arrays and to report on any events
1209 will never exit once it decides that there are arrays to be checked,
1210 so it should normally be run in the background.
1212 As well as reporting events,
1214 may move a spare drive from one array to another if they are in the
1217 and if the destination array has a failed drive but no spares.
1219 If any devices are listed on the command line,
1221 will only monitor those devices. Otherwise all arrays listed in the
1222 configuration file will be monitored. Further, if
1224 is given, then any other md devices that appear in
1226 will also be monitored.
1228 The result of monitoring the arrays is the generation of events.
1229 These events are passed to a separate program (if specified) and may
1230 be mailed to a given E-mail address.
1232 When passing event to program, the program is run once for each event
1233 and is given 2 or 3 command-line arguments. The first is the
1234 name of the event (see below). The second is the name of the
1235 md device which is affected, and the third is the name of a related
1236 device if relevant, such as a component device that has failed.
1240 is given, then a program or an E-mail address must be specified on the
1241 command line or in the config file. If neither are available, then
1243 will not monitor anything.
1247 will continue monitoring as long as something was found to monitor. If
1248 no program or email is given, then each event is reported to
1251 The different events are:
1255 .B DeviceDisappeared
1256 An md array which previously was configured appears to no longer be
1257 configured. (syslog priority: Critical)
1261 was told to monitor an array which is RAID0 or Linear, then it will
1263 .B DeviceDisappeared
1264 with the extra information
1266 This is because RAID0 and Linear do not support the device-failed,
1267 hot-spare and resync operations which are monitored.
1271 An md array started reconstruction. (syslog priority: Warning)
1277 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1278 percentage of the total. (syslog priority: Warning)
1282 An md array that was rebuilding, isn't any more, either because it
1283 finished normally or was aborted. (syslog priority: Warning)
1287 An active component device of an array has been marked as
1288 faulty. (syslog priority: Critical)
1292 A spare component device which was being rebuilt to replace a faulty
1293 device has failed. (syslog priority: Critial)
1297 A spare component device which was being rebuilt to replace a faulty
1298 device as been successfully rebuild and has been made active.
1299 (syslog priority: Info)
1303 A new md array has been detected in the
1305 file. (syslog priority: Info)
1309 A newly noticed array appears to be degraded. This message is not
1312 notices a drive failure which causes degradation, but only when
1314 notices that an array is degraded when it first sees the array.
1315 (syslog priority: Critial)
1319 A spare drive has been moved from one array in a
1321 to another to allow a failed drive to be replaced.
1322 (syslog priority: Info)
1328 has been told, via the config file, that an array should have a certain
1329 number of spare devices, and
1331 detects that it has fewer that this number when it first sees the
1332 array, it will report a
1335 (syslog priority: Info)
1339 An array was found at startup, and the
1342 (syslog priority: Info)
1351 cause Email to be sent. All events cause the program to be run.
1352 The program is run with two or three arguments, they being the event
1353 name, the array device and possibly a second device.
1355 Each event has an associated array device (e.g.
1357 and possibly a second device. For
1362 the second device is the relevant component device.
1365 the second device is the array that the spare was moved from.
1369 to move spares from one array to another, the different arrays need to
1370 be labelled with the same
1372 in the configuration file. The
1374 name can be any string. It is only necessary that different spare
1375 groups use different names.
1379 detects that an array which is in a spare group has fewer active
1380 devices than necessary for the complete array, and has no spare
1381 devices, it will look for another array in the same spare group that
1382 has a full complement of working drive and a spare. It will then
1383 attempt to remove the spare from the second drive and add it to the
1385 If the removal succeeds but the adding fails, then it is added back to
1389 The GROW mode is used for changing the size or shape of an active
1391 For this to work, the kernel must support the necessary change.
1392 Various types of growth are being added during 2.6 development,
1393 including restructuring a raid5 array to have more active devices.
1395 Currently the only support available is to
1397 change the "size" attribute
1398 for RAID1, RAID5 and RAID6.
1400 increase the "raid-disks" attribute of RAID1 and RAID5.
1402 add a write-intent bitmap to any array which support these bitmaps, or
1403 remove a write-intent bitmap from such an array.
1407 Normally when an array is built the "size" it taken from the smallest
1408 of the drives. If all the small drives in an arrays are, one at a
1409 time, removed and replaced with larger drives, then you could have an
1410 array of large drives with only a small amount used. In this
1411 situation, changing the "size" with "GROW" mode will allow the extra
1412 space to start being used. If the size is increased in this way, a
1413 "resync" process will start to make sure the new parts of the array
1416 Note that when an array changes size, any filesystem that may be
1417 stored in the array will not automatically grow to use the space. The
1418 filesystem will need to be explicitly told to use the extra space.
1420 .SS RAID-DEVICES CHANGES
1422 A RAID1 array can work with any number of devices from 1 upwards
1423 (though 1 is not very useful). There may be times which you want to
1424 increase or decrease the number of active devices. Note that this is
1425 different to hot-add or hot-remove which changes the number of
1428 When reducing the number of devices in a RAID1 array, the slots which
1429 are to be removed from the array must already be vacant. That is, the
1430 devices that which were in those slots must be failed and removed.
1432 When the number of devices is increased, any hot spares that are
1433 present will be activated immediately.
1435 Increasing the number of active devices in a RAID5 is much more
1436 effort. Every block in the array will need to be read and written
1437 back to a new location. From 2.6.17, the Linux Kernel is able to do
1438 this safely, including restart and interrupted "reshape".
1440 When relocating the first few stripes on a raid5, it is not possible
1441 to keep the data on disk completely consistent and crash-proof. To
1442 provide the required safety, mdadm disables writes to the array while
1443 this "critical section" is reshaped, and takes a backup of the data
1444 that is in that section. This backup is normally stored in any spare
1445 devices that the array has, however it can also be stored in a
1446 separate file specified with the
1448 option. If this option is used, and the system does crash during the
1449 critical period, the same file must be passed to
1451 to restore the backup and reassemble the array.
1455 A write-intent bitmap can be added to, or removed from, an active
1456 array. Either internal bitmaps, or bitmaps stored in a separate file
1457 can be added. Note that if you add a bitmap stored in a file which is
1458 in a filesystem that is on the raid array being affected, the system
1459 will deadlock. The bitmap must be on a separate filesystem.
1463 .B " mdadm --query /dev/name-of-device"
1465 This will find out if a given device is a raid array, or is part of
1466 one, and will provide brief information about the device.
1468 .B " mdadm --assemble --scan"
1470 This will assemble and start all arrays listed in the standard config file
1471 file. This command will typically go in a system startup file.
1473 .B " mdadm --stop --scan"
1475 This will shut down all array that can be shut down (i.e. are not
1476 currently in use). This will typically go in a system shutdown script.
1478 .B " mdadm --follow --scan --delay=120"
1480 If (and only if) there is an Email address or program given in the
1481 standard config file, then
1482 monitor the status of all arrays listed in that file by
1483 polling them ever 2 minutes.
1485 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1487 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1490 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1492 .B " mdadm --detail --scan >> mdadm.conf"
1494 This will create a prototype config file that describes currently
1495 active arrays that are known to be made from partitions of IDE or SCSI drives.
1496 This file should be reviewed before being used as it may
1497 contain unwanted detail.
1499 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1501 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1503 This will find what arrays could be assembled from existing IDE and
1504 SCSI whole drives (not partitions) and store the information is the
1505 format of a config file.
1506 This file is very likely to contain unwanted detail, particularly
1509 entries. It should be reviewed and edited before being used as an
1512 .B " mdadm --examine --brief --scan --config=partitions"
1514 .B " mdadm -Ebsc partitions"
1516 Create a list of devices by reading
1517 .BR /proc/partitions ,
1518 scan these for RAID superblocks, and printout a brief listing of all
1521 .B " mdadm -Ac partitions -m 0 /dev/md0"
1523 Scan all partitions and devices listed in
1524 .BR /proc/partitions
1527 out of all such devices with a RAID superblock with a minor number of 0.
1529 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1531 If config file contains a mail address or alert program, run mdadm in
1532 the background in monitor mode monitoring all md devices. Also write
1533 pid of mdadm daemon to
1534 .BR /var/run/mdadm .
1536 .B " mdadm --create --help"
1538 Provide help about the Create mode.
1540 .B " mdadm --config --help"
1542 Provide help about the format of the config file.
1546 Provide general help.
1557 lists all active md devices with information about them.
1559 uses this to find arrays when
1561 is given in Misc mode, and to monitor array reconstruction
1567 The config file lists which devices may be scanned to see if
1568 they contain MD super block, and gives identifying information
1569 (e.g. UUID) about known MD arrays. See
1575 While entries in the /dev directory can have any format you like,
1577 has an understanding of 'standard' formats which it uses to guide its
1578 behaviour when creating device files via the
1582 The standard names for non-partitioned arrays (the only sort of md
1583 array available in 2.4 and earlier) either of
1589 where NN is a number.
1590 The standard names for partitionable arrays (as available from 2.6
1597 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1601 was previously known as
1605 is completely separate from the
1607 package, and does not use the
1609 configuration file at all.
1612 For information on the various levels of
1616 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1617 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1620 '''for new releases of the RAID driver check out:
1623 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1624 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1629 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1630 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1633 The latest version of
1635 should always be available from
1637 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1638 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob