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 a 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 one of 'n', 'o' 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.
409 signals 'offset' copies. Rather than the chunks being duplicated
410 within a stripe, whole stripes are duplicated but are rotated by one
411 device so duplicate blocks are on different devices. Thus subsequent
412 copies of a block are in the next drive, and are one chunk further
417 (multiple copies have very different offsets). See md(4) for more
418 detail about 'near' and 'far'.
420 The number is the number of copies of each datablock. 2 is normal, 3
421 can be useful. This number can be at most equal to the number of
422 devices in the array. It does not need to divide evenly into that
423 number (e.g. it is perfectly legal to have an 'n2' layout for an array
424 with an odd number of devices).
428 same as --layout (thus explaining the p of
432 .BR -b ", " --bitmap=
433 Specify a file to store a write-intent bitmap in. The file should not
434 exist unless --force is also given. The same file should be provided
435 when assembling the array. If the word
437 is given, then the bitmap is stored with the metadata on the array,
438 and so is replicated on all devices. If the word
442 mode, then any bitmap that is present is removed.
444 To help catch typing errors, the filename must contain at least one
445 slash ('/') if it is a real file (not 'internal' or 'none').
447 Note: external bitmaps are only known to work on ext2 and ext3.
448 Storing bitmap files on other filesystems may result in serious problems.
452 Set the chunksize of the bitmap. Each bit corresponds to that many
453 Kilobytes of storage.
454 When using a file based bitmap, the default is to use the smallest
455 size that is atleast 4 and requires no more than 2^21 chunks.
458 bitmap, the chunksize is automatically determined to make best use of
463 .BR -W ", " --write-mostly
464 subsequent devices lists in a
469 command will be flagged as 'write-mostly'. This is valid for RAID1
470 only and means that the 'md' driver will avoid reading from these
471 devices if at all possible. This can be useful if mirroring over a
476 Specify that write-behind mode should be enabled (valid for RAID1
477 only). If an argument is specified, it will set the maximum number
478 of outstanding writes allowed. The default value is 256.
479 A write-intent bitmap is required in order to use write-behind
480 mode, and write-behind is only attempted on drives marked as
487 that the array pre-existed and is known to be clean. It can be useful
488 when trying to recover from a major failure as you can be sure that no
489 data will be affected unless you actually write to the array. It can
490 also be used when creating a RAID1 or RAID10 if you want to avoid the
491 initial resync, however this practice - while normally safe - is not
492 recommended. Use this ony if you really know what you are doing.
496 This is needed when --grow is used to increase the number of
497 raid-devices in a RAID5 if there are no spare devices available.
498 See the section below on RAID_DEVICE CHANGES. The file should be
499 stored on a separate device, not on the raid array being reshaped.
505 for the array. This is currently only effective when creating an
506 array with a version-1 superblock. The name is a simple textual
507 string that can be used to identify array components when assembling.
513 run the array, even if some of the components
514 appear to be active in another array or filesystem. Normally
516 will ask for confirmation before including such components in an
517 array. This option causes that question to be suppressed.
523 accept the geometry and layout specified without question. Normally
525 will not allow creation of an array with only one device, and will try
526 to create a raid5 array with one missing drive (as this makes the
527 initial resync work faster). With
530 will not try to be so clever.
533 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
534 Instruct mdadm to create the device file if needed, possibly allocating
535 an unused minor number. "md" causes a non-partitionable array
536 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
537 later) to be used. "yes" requires the named md device to have
538 a 'standard' format, and the type and minor number will be determined
539 from this. See DEVICE NAMES below.
541 The argument can also come immediately after
546 is also given, then any
548 entries in the config file will over-ride the
550 instruction given on the command line.
552 For partitionable arrays,
554 will create the device file for the whole array and for the first 4
555 partitions. A different number of partitions can be specified at the
556 end of this option (e.g.
558 If the device name ends with a digit, the partition names add a 'p',
559 and a number, e.g. "/dev/home1p3". If there is no
560 trailing digit, then the partition names just have a number added,
561 e.g. "/dev/scratch3".
563 If the md device name is in a 'standard' format as described in DEVICE
564 NAMES, then it will be created, if necessary, with the appropriate
565 number based on that name. If the device name is not in one of these
566 formats, then a unused minor number will be allocated. The minor
567 number will be considered unused if there is no active array for that
568 number, and there is no entry in /dev for that number and with a
575 uuid of array to assemble. Devices which don't have this uuid are
579 .BR -m ", " --super-minor=
580 Minor number of device that array was created for. Devices which
581 don't have this minor number are excluded. If you create an array as
582 /dev/md1, then all superblocks will contain the minor number 1, even if
583 the array is later assembled as /dev/md2.
585 Giving the literal word "dev" for
589 to use the minor number of the md device that is being assembled.
593 will look for super blocks with a minor number of 0.
597 Specify the name of the array to assemble. This must be the name
598 that was specified when creating the array.
602 Assemble the array even if some superblocks appear out-of-date
606 Attempt to start the array even if fewer drives were given than are
607 needed for a full array. Normally if not all drives are found and
609 is not used, then the array will be assembled but not started.
612 an attempt will be made to start it anyway.
615 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
616 See this option under Create and Build options.
619 .BR -b ", " --bitmap=
620 Specify the bitmap file that was given when the array was created. If
623 bitmap, there is no need to specify this when assembling the array.
629 was used to grow the number of raid-devices in a RAID5, and the system
630 crashed during the critical section, then the same
632 must be presented to --assemble to allow possibly corrupted data to be
636 .BR -U ", " --update=
637 Update the superblock on each device while assembling the array. The
638 argument given to this flag can be one of
649 option will adjust the superblock of an array what was created on a Sparc
650 machine running a patched 2.2 Linux kernel. This kernel got the
651 alignment of part of the superblock wrong. You can use the
652 .B "--examine --sparc2.2"
655 to see what effect this would have.
659 option will update the
661 field on each superblock to match the minor number of the array being
662 assembled. This is not needed on 2.6 and later kernels as they make
663 this adjustment automatically.
667 option will change the uuid of the array. If a UUID is given with the
668 "--uuid" option that UUID will be used as a new UUID and with
670 be used to help identify the devices in the array.
671 If no "--uuid" is given, a random uuid is chosen.
675 option will cause the array to be marked
677 meaning that any redundancy in the array (e.g. parity for raid5,
678 copies for raid1) may be incorrect. This will cause the raid system
679 to perform a "resync" pass to make sure that all redundant information
684 option allows arrays to be moved between machines with different
686 When assembling such an array for the first time after a move, giving
687 .B "--update=byteorder"
690 to expect superblocks to have their byteorder reversed, and will
691 correct that order before assembling the array. This is only valid
692 with original (Version 0.90) superblocks.
696 option will correct the summaries in the superblock. That is the
697 counts of total, working, active, failed, and spare devices.
703 hot-add listed devices.
707 re-add a device that was recently removed from an array.
711 remove listed devices. They must not be active. i.e. they should
712 be failed or spare devices.
716 mark listed devices as faulty.
723 Each of these options require that the first device list is the array
724 to be acted upon and the remainder are component devices to be added,
725 removed, or marked as fault. Several different operations can be
726 specified for different devices, e.g.
728 mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
730 Each operation applies to all devices listed until the next
733 If an array is using a write-intent bitmap, then devices which have
734 been removed can be re-added in a way that avoids a full
735 reconstruction but instead just updated the blocks that have changed
736 since the device was removed. For arrays with persistent metadata
737 (superblocks) this is done automatically. For arrays created with
739 mdadm needs to be told that this device we removed recently with
742 Devices can only be removed from an array if they are not in active
743 use. i.e. that must be spares or failed devices. To remove an active
744 device, it must be marked as
752 Examine a device to see
753 (1) if it is an md device and (2) if it is a component of an md
755 Information about what is discovered is presented.
759 Print detail of one or more md devices.
762 .BR -E ", " --examine
763 Print content of md superblock on device(s).
766 If an array was created on a 2.2 Linux kernel patched with RAID
767 support, the superblock will have been created incorrectly, or at
768 least incompatibly with 2.4 and later kernels. Using the
772 will fix the superblock before displaying it. If this appears to do
773 the right thing, then the array can be successfully assembled using
774 .BR "--assemble --update=sparc2.2" .
777 .BR -X ", " --examine-bitmap
778 Report information about a bitmap file.
782 start a partially built array.
786 deactivate array, releasing all resources.
789 .BR -o ", " --readonly
790 mark array as readonly.
793 .BR -w ", " --readwrite
794 mark array as readwrite.
798 If the device contains a valid md superblock, the block is
799 over-written with zeros. With
801 the block where the superblock would be is over-written even if it
802 doesn't appear to be valid.
810 is set to reflect the status of the device.
812 .SH For Monitor mode:
815 Give a mail address to send alerts to.
818 .BR -p ", " --program ", " --alert
819 Give a program to be run whenever an event is detected.
823 Cause all events to be reported through 'syslog'. The messages have
824 facility of 'daemon' and varying priorities.
828 Give a delay in seconds.
830 polls the md arrays and then waits this many seconds before polling
831 again. The default is 60 seconds.
834 .BR -f ", " --daemonise
837 to run as a background daemon if it decides to monitor anything. This
838 causes it to fork and run in the child, and to disconnect form the
839 terminal. The process id of the child is written to stdout.
842 which will only continue monitoring if a mail address or alert program
843 is found in the config file.
846 .BR -i ", " --pid-file
849 is running in daemon mode, write the pid of the daemon process to
850 the specified file, instead of printing it on standard output.
853 .BR -1 ", " --oneshot
854 Check arrays only once. This will generate
856 events and more significantly
862 .B " mdadm --monitor --scan -1"
864 from a cron script will ensure regular notification of any degraded arrays.
870 alert for every array found at startup. This alert gets mailed and
871 passed to the alert program. This can be used for testing that alert
872 message do get through successfully.
879 .I md-device options-and-component-devices...
882 .B mdadm --assemble --scan
883 .I md-devices-and-options...
886 .B mdadm --assemble --scan
890 This usage assembles one or more raid arrays from pre-existing components.
891 For each array, mdadm needs to know the md device, the identity of the
892 array, and a number of component-devices. These can be found in a number of ways.
894 In the first usage example (without the
896 the first device given is the md device.
897 In the second usage example, all devices listed are treated as md
898 devices and assembly is attempted.
899 In the third (where no devices are listed) all md devices that are
900 listed in the configuration file are assembled.
902 If precisely one device is listed, but
908 was given and identify information is extracted from the configuration file.
910 The identity can be given with the
914 option, can be found in the config file, or will be taken from the
915 super block on the first component-device listed on the command line.
917 Devices can be given on the
919 command line or in the config file. Only devices which have an md
920 superblock which contains the right identity will be considered for
923 The config file is only used if explicitly named with
925 or requested with (a possibly implicit)
933 is not given, then the config file will only be used to find the
934 identity of md arrays.
936 Normally the array will be started after it is assembled. However if
938 is not given and insufficient drives were listed to start a complete
939 (non-degraded) array, then the array is not started (to guard against
940 usage errors). To insist that the array be started in this case (as
941 may work for RAID1, 4, 5, 6, or 10), give the
947 option is given, either on the command line (--auto) or in the
948 configuration file (e.g. auto=part), then
950 will create the md device if necessary or will re-create it if it
951 doesn't look usable as it is.
953 This can be useful for handling partitioned devices (which don't have
954 a stable device number - it can change after a reboot) and when using
955 "udev" to manage your
957 tree (udev cannot handle md devices because of the unusual device
958 initialisation conventions).
960 If the option to "auto" is "mdp" or "part" or (on the command line
961 only) "p", then mdadm will create a partitionable array, using the
962 first free one that is not in use, and does not already have an entry
963 in /dev (apart from numeric /dev/md* entries).
965 If the option to "auto" is "yes" or "md" or (on the command line)
966 nothing, then mdadm will create a traditional, non-partitionable md
969 It is expected that the "auto" functionality will be used to create
970 device entries with meaningful names such as "/dev/md/home" or
971 "/dev/md/root", rather than names based on the numerical array number.
973 When using this option to create a partitionable array, the device
974 files for the first 4 partitions are also created. If a different
975 number is required it can be simply appended to the auto option.
976 e.g. "auto=part8". Partition names are created by appending a digit
977 string to the device name, with an intervening "p" if the device name
982 option is also available in Build and Create modes. As those modes do
983 not use a config file, the "auto=" config option does not apply to
994 .BI --raid-devices= Z
998 This usage is similar to
1000 The difference is that it creates an array without a superblock. With
1001 these arrays there is no difference between initially creating the array and
1002 subsequently assembling the array, except that hopefully there is useful
1003 data there in the second case.
1005 The level may raid0, linear, multipath, or faulty, or one of their
1006 synonyms. All devices must be listed and the array will be started
1018 .BI --raid-devices= Z
1022 This usage will initialise a new md array, associate some devices with
1023 it, and activate the array.
1027 option is given (as described in more detail in the section on
1028 Assemble mode), then the md device will be created with a suitable
1029 device number if necessary.
1031 As devices are added, they are checked to see if they contain raid
1032 superblocks or filesystems. They are also checked to see if the variance in
1033 device size exceeds 1%.
1035 If any discrepancy is found, the array will not automatically be run, though
1038 can override this caution.
1040 To create a "degraded" array in which some devices are missing, simply
1041 give the word "\fBmissing\fP"
1042 in place of a device name. This will cause
1044 to leave the corresponding slot in the array empty.
1045 For a RAID4 or RAID5 array at most one slot can be
1046 "\fBmissing\fP"; for a RAID6 array at most two slots.
1047 For a RAID1 array, only one real device needs to be given. All of the
1051 When creating a RAID5 array,
1053 will automatically create a degraded array with an extra spare drive.
1054 This is because building the spare into a degraded array is in general faster than resyncing
1055 the parity on a non-degraded, but not clean, array. This feature can
1056 be over-ridden with the
1062 '''option is given, it is not necessary to list any component-devices in this command.
1063 '''They can be added later, before a
1067 '''is given, the apparent size of the smallest drive given is used.
1069 The General Management options that are valid with --create are:
1072 insist on running the array even if some devices look like they might
1077 start the array readonly - not supported yet.
1085 .I options... devices...
1088 This usage will allow individual devices in an array to be failed,
1089 removed or added. It is possible to perform multiple operations with
1090 on command. For example:
1092 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1098 and will then remove it from the array and finally add it back
1099 in as a spare. However only one md array can be affected by a single
1110 MISC mode includes a number of distinct operations that
1111 operate on distinct devices. The operations are:
1114 The device is examined to see if it is
1115 (1) an active md array, or
1116 (2) a component of an md array.
1117 The information discovered is reported.
1121 The device should be an active md device.
1123 will display a detailed description of the array.
1127 will cause the output to be less detailed and the format to be
1128 suitable for inclusion in
1129 .BR /etc/mdadm.conf .
1132 will normally be 0 unless
1134 failed to get useful information about the device(s). However if the
1136 option is given, then the exit status will be:
1140 The array is functioning normally.
1143 The array has at least one failed device.
1146 The array has multiple failed devices and hence is unusable (raid4 or
1150 There was an error while trying to get information about the device.
1155 The device should be a component of an md array.
1157 will read the md superblock of the device and display the contents.
1162 then multiple devices that are components of the one array
1163 are grouped together and reported in a single entry suitable
1165 .BR /etc/mdadm.conf .
1169 without listing any devices will cause all devices listed in the
1170 config file to be examined.
1174 The devices should be active md arrays which will be deactivated, as
1175 long as they are not currently in use.
1179 This will fully activate a partially assembled md array.
1183 This will mark an active array as read-only, providing that it is
1184 not currently being used.
1190 array back to being read/write.
1194 For all operations except
1197 will cause the operation to be applied to all arrays listed in
1202 causes all devices listed in the config file to be examined.
1210 .I options... devices...
1215 to periodically poll a number of md arrays and to report on any events
1218 will never exit once it decides that there are arrays to be checked,
1219 so it should normally be run in the background.
1221 As well as reporting events,
1223 may move a spare drive from one array to another if they are in the
1226 and if the destination array has a failed drive but no spares.
1228 If any devices are listed on the command line,
1230 will only monitor those devices. Otherwise all arrays listed in the
1231 configuration file will be monitored. Further, if
1233 is given, then any other md devices that appear in
1235 will also be monitored.
1237 The result of monitoring the arrays is the generation of events.
1238 These events are passed to a separate program (if specified) and may
1239 be mailed to a given E-mail address.
1241 When passing event to program, the program is run once for each event
1242 and is given 2 or 3 command-line arguments. The first is the
1243 name of the event (see below). The second is the name of the
1244 md device which is affected, and the third is the name of a related
1245 device if relevant, such as a component device that has failed.
1249 is given, then a program or an E-mail address must be specified on the
1250 command line or in the config file. If neither are available, then
1252 will not monitor anything.
1256 will continue monitoring as long as something was found to monitor. If
1257 no program or email is given, then each event is reported to
1260 The different events are:
1264 .B DeviceDisappeared
1265 An md array which previously was configured appears to no longer be
1266 configured. (syslog priority: Critical)
1270 was told to monitor an array which is RAID0 or Linear, then it will
1272 .B DeviceDisappeared
1273 with the extra information
1275 This is because RAID0 and Linear do not support the device-failed,
1276 hot-spare and resync operations which are monitored.
1280 An md array started reconstruction. (syslog priority: Warning)
1286 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1287 percentage of the total. (syslog priority: Warning)
1291 An md array that was rebuilding, isn't any more, either because it
1292 finished normally or was aborted. (syslog priority: Warning)
1296 An active component device of an array has been marked as
1297 faulty. (syslog priority: Critical)
1301 A spare component device which was being rebuilt to replace a faulty
1302 device has failed. (syslog priority: Critial)
1306 A spare component device which was being rebuilt to replace a faulty
1307 device has been successfully rebuilt and has been made active.
1308 (syslog priority: Info)
1312 A new md array has been detected in the
1314 file. (syslog priority: Info)
1318 A newly noticed array appears to be degraded. This message is not
1321 notices a drive failure which causes degradation, but only when
1323 notices that an array is degraded when it first sees the array.
1324 (syslog priority: Critial)
1328 A spare drive has been moved from one array in a
1330 to another to allow a failed drive to be replaced.
1331 (syslog priority: Info)
1337 has been told, via the config file, that an array should have a certain
1338 number of spare devices, and
1340 detects that it has fewer that this number when it first sees the
1341 array, it will report a
1344 (syslog priority: Warning)
1348 An array was found at startup, and the
1351 (syslog priority: Info)
1361 cause Email to be sent. All events cause the program to be run.
1362 The program is run with two or three arguments, they being the event
1363 name, the array device and possibly a second device.
1365 Each event has an associated array device (e.g.
1367 and possibly a second device. For
1372 the second device is the relevant component device.
1375 the second device is the array that the spare was moved from.
1379 to move spares from one array to another, the different arrays need to
1380 be labelled with the same
1382 in the configuration file. The
1384 name can be any string. It is only necessary that different spare
1385 groups use different names.
1389 detects that an array which is in a spare group has fewer active
1390 devices than necessary for the complete array, and has no spare
1391 devices, it will look for another array in the same spare group that
1392 has a full complement of working drive and a spare. It will then
1393 attempt to remove the spare from the second drive and add it to the
1395 If the removal succeeds but the adding fails, then it is added back to
1399 The GROW mode is used for changing the size or shape of an active
1401 For this to work, the kernel must support the necessary change.
1402 Various types of growth are being added during 2.6 development,
1403 including restructuring a raid5 array to have more active devices.
1405 Currently the only support available is to
1407 change the "size" attribute
1408 for RAID1, RAID5 and RAID6.
1410 increase the "raid-disks" attribute of RAID1 and RAID5.
1412 add a write-intent bitmap to any array which support these bitmaps, or
1413 remove a write-intent bitmap from such an array.
1417 Normally when an array is built the "size" it taken from the smallest
1418 of the drives. If all the small drives in an arrays are, one at a
1419 time, removed and replaced with larger drives, then you could have an
1420 array of large drives with only a small amount used. In this
1421 situation, changing the "size" with "GROW" mode will allow the extra
1422 space to start being used. If the size is increased in this way, a
1423 "resync" process will start to make sure the new parts of the array
1426 Note that when an array changes size, any filesystem that may be
1427 stored in the array will not automatically grow to use the space. The
1428 filesystem will need to be explicitly told to use the extra space.
1430 .SS RAID-DEVICES CHANGES
1432 A RAID1 array can work with any number of devices from 1 upwards
1433 (though 1 is not very useful). There may be times which you want to
1434 increase or decrease the number of active devices. Note that this is
1435 different to hot-add or hot-remove which changes the number of
1438 When reducing the number of devices in a RAID1 array, the slots which
1439 are to be removed from the array must already be vacant. That is, the
1440 devices that which were in those slots must be failed and removed.
1442 When the number of devices is increased, any hot spares that are
1443 present will be activated immediately.
1445 Increasing the number of active devices in a RAID5 is much more
1446 effort. Every block in the array will need to be read and written
1447 back to a new location. From 2.6.17, the Linux Kernel is able to do
1448 this safely, including restart and interrupted "reshape".
1450 When relocating the first few stripes on a raid5, it is not possible
1451 to keep the data on disk completely consistent and crash-proof. To
1452 provide the required safety, mdadm disables writes to the array while
1453 this "critical section" is reshaped, and takes a backup of the data
1454 that is in that section. This backup is normally stored in any spare
1455 devices that the array has, however it can also be stored in a
1456 separate file specified with the
1458 option. If this option is used, and the system does crash during the
1459 critical period, the same file must be passed to
1461 to restore the backup and reassemble the array.
1465 A write-intent bitmap can be added to, or removed from, an active
1466 array. Either internal bitmaps, or bitmaps stored in a separate file
1467 can be added. Note that if you add a bitmap stored in a file which is
1468 in a filesystem that is on the raid array being affected, the system
1469 will deadlock. The bitmap must be on a separate filesystem.
1473 .B " mdadm --query /dev/name-of-device"
1475 This will find out if a given device is a raid array, or is part of
1476 one, and will provide brief information about the device.
1478 .B " mdadm --assemble --scan"
1480 This will assemble and start all arrays listed in the standard config file
1481 file. This command will typically go in a system startup file.
1483 .B " mdadm --stop --scan"
1485 This will shut down all array that can be shut down (i.e. are not
1486 currently in use). This will typically go in a system shutdown script.
1488 .B " mdadm --follow --scan --delay=120"
1490 If (and only if) there is an Email address or program given in the
1491 standard config file, then
1492 monitor the status of all arrays listed in that file by
1493 polling them ever 2 minutes.
1495 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1497 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1500 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1502 .B " mdadm --detail --scan >> mdadm.conf"
1504 This will create a prototype config file that describes currently
1505 active arrays that are known to be made from partitions of IDE or SCSI drives.
1506 This file should be reviewed before being used as it may
1507 contain unwanted detail.
1509 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1511 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1513 This will find what arrays could be assembled from existing IDE and
1514 SCSI whole drives (not partitions) and store the information is the
1515 format of a config file.
1516 This file is very likely to contain unwanted detail, particularly
1519 entries. It should be reviewed and edited before being used as an
1522 .B " mdadm --examine --brief --scan --config=partitions"
1524 .B " mdadm -Ebsc partitions"
1526 Create a list of devices by reading
1527 .BR /proc/partitions ,
1528 scan these for RAID superblocks, and printout a brief listing of all
1531 .B " mdadm -Ac partitions -m 0 /dev/md0"
1533 Scan all partitions and devices listed in
1534 .BR /proc/partitions
1537 out of all such devices with a RAID superblock with a minor number of 0.
1539 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1541 If config file contains a mail address or alert program, run mdadm in
1542 the background in monitor mode monitoring all md devices. Also write
1543 pid of mdadm daemon to
1544 .BR /var/run/mdadm .
1546 .B " mdadm --create --help"
1548 Provide help about the Create mode.
1550 .B " mdadm --config --help"
1552 Provide help about the format of the config file.
1556 Provide general help.
1567 lists all active md devices with information about them.
1569 uses this to find arrays when
1571 is given in Misc mode, and to monitor array reconstruction
1577 The config file lists which devices may be scanned to see if
1578 they contain MD super block, and gives identifying information
1579 (e.g. UUID) about known MD arrays. See
1585 While entries in the /dev directory can have any format you like,
1587 has an understanding of 'standard' formats which it uses to guide its
1588 behaviour when creating device files via the
1592 The standard names for non-partitioned arrays (the only sort of md
1593 array available in 2.4 and earlier) either of
1599 where NN is a number.
1600 The standard names for partitionable arrays (as available from 2.6
1607 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1611 was previously known as
1615 is completely separate from the
1617 package, and does not use the
1619 configuration file at all.
1622 For information on the various levels of
1626 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1627 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1630 '''for new releases of the RAID driver check out:
1633 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1634 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1639 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1640 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1643 The latest version of
1645 should always be available from
1647 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1648 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob