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 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.
453 Set the chunksize of the bitmap. Each bit corresponds to that many
454 Kilobytes of storage. Default is 4 when using a file based bitmap.
457 bitmap, the chunksize is automatically determined to make best use of
462 .BR -W ", " --write-mostly
463 subsequent devices lists in a
468 command will be flagged as 'write-mostly'. This is valid for RAID1
469 only and means that the 'md' driver will avoid reading from these
470 devices if at all possible. This can be useful if mirroring over a
475 Specify that write-behind mode should be enabled (valid for RAID1
476 only). If an argument is specified, it will set the maximum number
477 of outstanding writes allowed. The default value is 256.
478 A write-intent bitmap is required in order to use write-behind
479 mode, and write-behind is only attempted on drives marked as
486 that the array pre-existed and is known to be clean. It can be useful
487 when trying to recover from a major failure as you can be sure that no
488 data will be affected unless you actually write to the array. It can
489 also be used when creating a RAID1 or RAID10 if you want to avoid the
490 initial resync, however this practice - while normally safe - is not
491 recommended. Use this ony if you really know what you are doing.
495 This is needed when --grow is used to increase the number of
496 raid-devices in a RAID5 if there are no spare devices available.
497 See the section below on RAID_DEVICE CHANGES. The file should be
498 stored on a separate device, not on the raid array being reshaped.
504 for the array. This is currently only effective when creating an
505 array with a version-1 superblock. The name is a simple textual
506 string that can be used to identify array components when assembling.
512 run the array, even if some of the components
513 appear to be active in another array or filesystem. Normally
515 will ask for confirmation before including such components in an
516 array. This option causes that question to be suppressed.
522 accept the geometry and layout specified without question. Normally
524 will not allow creation of an array with only one device, and will try
525 to create a raid5 array with one missing drive (as this makes the
526 initial resync work faster). With
529 will not try to be so clever.
532 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
533 Instruct mdadm to create the device file if needed, possibly allocating
534 an unused minor number. "md" causes a non-partitionable array
535 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
536 later) to be used. "yes" requires the named md device to have
537 a 'standard' format, and the type and minor number will be determined
538 from this. See DEVICE NAMES below.
540 The argument can also come immediately after
545 is also given, then any
547 entries in the config file will over-ride the
549 instruction given on the command line.
551 For partitionable arrays,
553 will create the device file for the whole array and for the first 4
554 partitions. A different number of partitions can be specified at the
555 end of this option (e.g.
557 If the device name ends with a digit, the partition names add a 'p',
558 and a number, e.g. "/dev/home1p3". If there is no
559 trailing digit, then the partition names just have a number added,
560 e.g. "/dev/scratch3".
562 If the md device name is in a 'standard' format as described in DEVICE
563 NAMES, then it will be created, if necessary, with the appropriate
564 number based on that name. If the device name is not in one of these
565 formats, then a unused minor number will be allocated. The minor
566 number will be considered unused if there is no active array for that
567 number, and there is no entry in /dev for that number and with a
574 uuid of array to assemble. Devices which don't have this uuid are
578 .BR -m ", " --super-minor=
579 Minor number of device that array was created for. Devices which
580 don't have this minor number are excluded. If you create an array as
581 /dev/md1, then all superblocks will contain the minor number 1, even if
582 the array is later assembled as /dev/md2.
584 Giving the literal word "dev" for
588 to use the minor number of the md device that is being assembled.
592 will look for super blocks with a minor number of 0.
596 Specify the name of the array to assemble. This must be the name
597 that was specified when creating the array.
601 Assemble the array even if some superblocks appear out-of-date
605 Attempt to start the array even if fewer drives were given than are
606 needed for a full array. Normally if not all drives are found and
608 is not used, then the array will be assembled but not started.
611 an attempt will be made to start it anyway.
614 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
615 See this option under Create and Build options.
618 .BR -b ", " --bitmap=
619 Specify the bitmap file that was given when the array was created. If
622 bitmap, there is no need to specify this when assembling the array.
628 was used to grow the number of raid-devices in a RAID5, and the system
629 crashed during the critical section, then the same
631 must be presented to --assemble to allow possibly corrupted data to be
635 .BR -U ", " --update=
636 Update the superblock on each device while assembling the array. The
637 argument given to this flag can be one of
648 option will adjust the superblock of an array what was created on a Sparc
649 machine running a patched 2.2 Linux kernel. This kernel got the
650 alignment of part of the superblock wrong. You can use the
651 .B "--examine --sparc2.2"
654 to see what effect this would have.
658 option will update the
660 field on each superblock to match the minor number of the array being
661 assembled. This is not needed on 2.6 and later kernels as they make
662 this adjustment automatically.
666 option will change the uuid of the array. If a UUID is given with the
667 "--uuid" option that UUID will be used as a new UUID and with
669 be used to help identify the devices in the array.
670 If no "--uuid" is given, a random uuid is chosen.
674 option will cause the array to be marked
676 meaning that any redundancy in the array (e.g. parity for raid5,
677 copies for raid1) may be incorrect. This will cause the raid system
678 to perform a "resync" pass to make sure that all redundant information
683 option allows arrays to be moved between machines with different
685 When assembling such an array for the first time after a move, giving
686 .B "--update=byteorder"
689 to expect superblocks to have their byteorder reversed, and will
690 correct that order before assembling the array. This is only valid
691 with original (Version 0.90) superblocks.
695 option will correct the summaries in the superblock. That is the
696 counts of total, working, active, failed, and spare devices.
702 hot-add listed devices.
706 re-add a device that was recently removed from an array.
710 remove listed devices. They must not be active. i.e. they should
711 be failed or spare devices.
715 mark listed devices as faulty.
722 Each of these options require that the first device list is the array
723 to be acted upon and the remainder are component devices to be added,
724 removed, or marked as fault. Several different operations can be
725 specified for different devices, e.g.
727 mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
729 Each operation applies to all devices listed until the next
732 If an array is using a write-intent bitmap, then devices which have
733 been removed can be re-added in a way that avoids a full
734 reconstruction but instead just updated the blocks that have changed
735 since the device was removed. For arrays with persistent metadata
736 (superblocks) this is done automatically. For arrays created with
738 mdadm needs to be told that this device we removed recently with
741 Devices can only be removed from an array if they are not in active
742 use. i.e. that must be spares or failed devices. To remove an active
743 device, it must be marked as
751 Examine a device to see
752 (1) if it is an md device and (2) if it is a component of an md
754 Information about what is discovered is presented.
758 Print detail of one or more md devices.
761 .BR -E ", " --examine
762 Print content of md superblock on device(s).
765 If an array was created on a 2.2 Linux kernel patched with RAID
766 support, the superblock will have been created incorrectly, or at
767 least incompatibly with 2.4 and later kernels. Using the
771 will fix the superblock before displaying it. If this appears to do
772 the right thing, then the array can be successfully assembled using
773 .BR "--assemble --update=sparc2.2" .
776 .BR -X ", " --examine-bitmap
777 Report information about a bitmap file.
781 start a partially built array.
785 deactivate array, releasing all resources.
788 .BR -o ", " --readonly
789 mark array as readonly.
792 .BR -w ", " --readwrite
793 mark array as readwrite.
797 If the device contains a valid md superblock, the block is
798 over-written with zeros. With
800 the block where the superblock would be is over-written even if it
801 doesn't appear to be valid.
809 is set to reflect the status of the device.
811 .SH For Monitor mode:
814 Give a mail address to send alerts to.
817 .BR -p ", " --program ", " --alert
818 Give a program to be run whenever an event is detected.
822 Cause all events to be reported through 'syslog'. The messages have
823 facility of 'daemon' and varying priorities.
827 Give a delay in seconds.
829 polls the md arrays and then waits this many seconds before polling
830 again. The default is 60 seconds.
833 .BR -f ", " --daemonise
836 to run as a background daemon if it decides to monitor anything. This
837 causes it to fork and run in the child, and to disconnect form the
838 terminal. The process id of the child is written to stdout.
841 which will only continue monitoring if a mail address or alert program
842 is found in the config file.
845 .BR -i ", " --pid-file
848 is running in daemon mode, write the pid of the daemon process to
849 the specified file, instead of printing it on standard output.
852 .BR -1 ", " --oneshot
853 Check arrays only once. This will generate
855 events and more significantly
861 .B " mdadm --monitor --scan -1"
863 from a cron script will ensure regular notification of any degraded arrays.
869 alert for every array found at startup. This alert gets mailed and
870 passed to the alert program. This can be used for testing that alert
871 message do get through successfully.
878 .I md-device options-and-component-devices...
881 .B mdadm --assemble --scan
882 .I md-devices-and-options...
885 .B mdadm --assemble --scan
889 This usage assembles one or more raid arrays from pre-existing components.
890 For each array, mdadm needs to know the md device, the identity of the
891 array, and a number of component-devices. These can be found in a number of ways.
893 In the first usage example (without the
895 the first device given is the md device.
896 In the second usage example, all devices listed are treated as md
897 devices and assembly is attempted.
898 In the third (where no devices are listed) all md devices that are
899 listed in the configuration file are assembled.
901 If precisely one device is listed, but
907 was given and identify information is extracted from the configuration file.
909 The identity can be given with the
913 option, can be found in the config file, or will be taken from the
914 super block on the first component-device listed on the command line.
916 Devices can be given on the
918 command line or in the config file. Only devices which have an md
919 superblock which contains the right identity will be considered for
922 The config file is only used if explicitly named with
924 or requested with (a possibly implicit)
932 is not given, then the config file will only be used to find the
933 identity of md arrays.
935 Normally the array will be started after it is assembled. However if
937 is not given and insufficient drives were listed to start a complete
938 (non-degraded) array, then the array is not started (to guard against
939 usage errors). To insist that the array be started in this case (as
940 may work for RAID1, 4, 5, 6, or 10), give the
946 option is given, either on the command line (--auto) or in the
947 configuration file (e.g. auto=part), then
949 will create the md device if necessary or will re-create it if it
950 doesn't look usable as it is.
952 This can be useful for handling partitioned devices (which don't have
953 a stable device number - it can change after a reboot) and when using
954 "udev" to manage your
956 tree (udev cannot handle md devices because of the unusual device
957 initialisation conventions).
959 If the option to "auto" is "mdp" or "part" or (on the command line
960 only) "p", then mdadm will create a partitionable array, using the
961 first free one that is not in use, and does not already have an entry
962 in /dev (apart from numeric /dev/md* entries).
964 If the option to "auto" is "yes" or "md" or (on the command line)
965 nothing, then mdadm will create a traditional, non-partitionable md
968 It is expected that the "auto" functionality will be used to create
969 device entries with meaningful names such as "/dev/md/home" or
970 "/dev/md/root", rather than names based on the numerical array number.
972 When using this option to create a partitionable array, the device
973 files for the first 4 partitions are also created. If a different
974 number is required it can be simply appended to the auto option.
975 e.g. "auto=part8". Partition names are created by appending a digit
976 string to the device name, with an intervening "p" if the device name
981 option is also available in Build and Create modes. As those modes do
982 not use a config file, the "auto=" config option does not apply to
993 .BI --raid-devices= Z
997 This usage is similar to
999 The difference is that it creates an array without a superblock. With
1000 these arrays there is no difference between initially creating the array and
1001 subsequently assembling the array, except that hopefully there is useful
1002 data there in the second case.
1004 The level may raid0, linear, multipath, or faulty, or one of their
1005 synonyms. All devices must be listed and the array will be started
1017 .BI --raid-devices= Z
1021 This usage will initialise a new md array, associate some devices with
1022 it, and activate the array.
1026 option is given (as described in more detail in the section on
1027 Assemble mode), then the md device will be created with a suitable
1028 device number if necessary.
1030 As devices are added, they are checked to see if they contain raid
1031 superblocks or filesystems. They are also checked to see if the variance in
1032 device size exceeds 1%.
1034 If any discrepancy is found, the array will not automatically be run, though
1037 can override this caution.
1039 To create a "degraded" array in which some devices are missing, simply
1040 give the word "\fBmissing\fP"
1041 in place of a device name. This will cause
1043 to leave the corresponding slot in the array empty.
1044 For a RAID4 or RAID5 array at most one slot can be
1045 "\fBmissing\fP"; for a RAID6 array at most two slots.
1046 For a RAID1 array, only one real device needs to be given. All of the
1050 When creating a RAID5 array,
1052 will automatically create a degraded array with an extra spare drive.
1053 This is because building the spare into a degraded array is in general faster than resyncing
1054 the parity on a non-degraded, but not clean, array. This feature can
1055 be over-ridden with the
1061 '''option is given, it is not necessary to list any component-devices in this command.
1062 '''They can be added later, before a
1066 '''is given, the apparent size of the smallest drive given is used.
1068 The General Management options that are valid with --create are:
1071 insist on running the array even if some devices look like they might
1076 start the array readonly - not supported yet.
1084 .I options... devices...
1087 This usage will allow individual devices in an array to be failed,
1088 removed or added. It is possible to perform multiple operations with
1089 on command. For example:
1091 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1097 and will then remove it from the array and finally add it back
1098 in as a spare. However only one md array can be affected by a single
1109 MISC mode includes a number of distinct operations that
1110 operate on distinct devices. The operations are:
1113 The device is examined to see if it is
1114 (1) an active md array, or
1115 (2) a component of an md array.
1116 The information discovered is reported.
1120 The device should be an active md device.
1122 will display a detailed description of the array.
1126 will cause the output to be less detailed and the format to be
1127 suitable for inclusion in
1128 .BR /etc/mdadm.conf .
1131 will normally be 0 unless
1133 failed to get useful information about the device(s). However if the
1135 option is given, then the exit status will be:
1139 The array is functioning normally.
1142 The array has at least one failed device.
1145 The array has multiple failed devices and hence is unusable (raid4 or
1149 There was an error while trying to get information about the device.
1154 The device should be a component of an md array.
1156 will read the md superblock of the device and display the contents.
1161 then multiple devices that are components of the one array
1162 are grouped together and reported in a single entry suitable
1164 .BR /etc/mdadm.conf .
1168 without listing any devices will cause all devices listed in the
1169 config file to be examined.
1173 The devices should be active md arrays which will be deactivated, as
1174 long as they are not currently in use.
1178 This will fully activate a partially assembled md array.
1182 This will mark an active array as read-only, providing that it is
1183 not currently being used.
1189 array back to being read/write.
1193 For all operations except
1196 will cause the operation to be applied to all arrays listed in
1201 causes all devices listed in the config file to be examined.
1209 .I options... devices...
1214 to periodically poll a number of md arrays and to report on any events
1217 will never exit once it decides that there are arrays to be checked,
1218 so it should normally be run in the background.
1220 As well as reporting events,
1222 may move a spare drive from one array to another if they are in the
1225 and if the destination array has a failed drive but no spares.
1227 If any devices are listed on the command line,
1229 will only monitor those devices. Otherwise all arrays listed in the
1230 configuration file will be monitored. Further, if
1232 is given, then any other md devices that appear in
1234 will also be monitored.
1236 The result of monitoring the arrays is the generation of events.
1237 These events are passed to a separate program (if specified) and may
1238 be mailed to a given E-mail address.
1240 When passing event to program, the program is run once for each event
1241 and is given 2 or 3 command-line arguments. The first is the
1242 name of the event (see below). The second is the name of the
1243 md device which is affected, and the third is the name of a related
1244 device if relevant, such as a component device that has failed.
1248 is given, then a program or an E-mail address must be specified on the
1249 command line or in the config file. If neither are available, then
1251 will not monitor anything.
1255 will continue monitoring as long as something was found to monitor. If
1256 no program or email is given, then each event is reported to
1259 The different events are:
1263 .B DeviceDisappeared
1264 An md array which previously was configured appears to no longer be
1265 configured. (syslog priority: Critical)
1269 was told to monitor an array which is RAID0 or Linear, then it will
1271 .B DeviceDisappeared
1272 with the extra information
1274 This is because RAID0 and Linear do not support the device-failed,
1275 hot-spare and resync operations which are monitored.
1279 An md array started reconstruction. (syslog priority: Warning)
1285 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1286 percentage of the total. (syslog priority: Warning)
1290 An md array that was rebuilding, isn't any more, either because it
1291 finished normally or was aborted. (syslog priority: Warning)
1295 An active component device of an array has been marked as
1296 faulty. (syslog priority: Critical)
1300 A spare component device which was being rebuilt to replace a faulty
1301 device has failed. (syslog priority: Critial)
1305 A spare component device which was being rebuilt to replace a faulty
1306 device as been successfully rebuild and has been made active.
1307 (syslog priority: Info)
1311 A new md array has been detected in the
1313 file. (syslog priority: Info)
1317 A newly noticed array appears to be degraded. This message is not
1320 notices a drive failure which causes degradation, but only when
1322 notices that an array is degraded when it first sees the array.
1323 (syslog priority: Critial)
1327 A spare drive has been moved from one array in a
1329 to another to allow a failed drive to be replaced.
1330 (syslog priority: Info)
1336 has been told, via the config file, that an array should have a certain
1337 number of spare devices, and
1339 detects that it has fewer that this number when it first sees the
1340 array, it will report a
1343 (syslog priority: Warning)
1347 An array was found at startup, and the
1350 (syslog priority: Info)
1360 cause Email to be sent. All events cause the program to be run.
1361 The program is run with two or three arguments, they being the event
1362 name, the array device and possibly a second device.
1364 Each event has an associated array device (e.g.
1366 and possibly a second device. For
1371 the second device is the relevant component device.
1374 the second device is the array that the spare was moved from.
1378 to move spares from one array to another, the different arrays need to
1379 be labelled with the same
1381 in the configuration file. The
1383 name can be any string. It is only necessary that different spare
1384 groups use different names.
1388 detects that an array which is in a spare group has fewer active
1389 devices than necessary for the complete array, and has no spare
1390 devices, it will look for another array in the same spare group that
1391 has a full complement of working drive and a spare. It will then
1392 attempt to remove the spare from the second drive and add it to the
1394 If the removal succeeds but the adding fails, then it is added back to
1398 The GROW mode is used for changing the size or shape of an active
1400 For this to work, the kernel must support the necessary change.
1401 Various types of growth are being added during 2.6 development,
1402 including restructuring a raid5 array to have more active devices.
1404 Currently the only support available is to
1406 change the "size" attribute
1407 for RAID1, RAID5 and RAID6.
1409 increase the "raid-disks" attribute of RAID1 and RAID5.
1411 add a write-intent bitmap to any array which support these bitmaps, or
1412 remove a write-intent bitmap from such an array.
1416 Normally when an array is built the "size" it taken from the smallest
1417 of the drives. If all the small drives in an arrays are, one at a
1418 time, removed and replaced with larger drives, then you could have an
1419 array of large drives with only a small amount used. In this
1420 situation, changing the "size" with "GROW" mode will allow the extra
1421 space to start being used. If the size is increased in this way, a
1422 "resync" process will start to make sure the new parts of the array
1425 Note that when an array changes size, any filesystem that may be
1426 stored in the array will not automatically grow to use the space. The
1427 filesystem will need to be explicitly told to use the extra space.
1429 .SS RAID-DEVICES CHANGES
1431 A RAID1 array can work with any number of devices from 1 upwards
1432 (though 1 is not very useful). There may be times which you want to
1433 increase or decrease the number of active devices. Note that this is
1434 different to hot-add or hot-remove which changes the number of
1437 When reducing the number of devices in a RAID1 array, the slots which
1438 are to be removed from the array must already be vacant. That is, the
1439 devices that which were in those slots must be failed and removed.
1441 When the number of devices is increased, any hot spares that are
1442 present will be activated immediately.
1444 Increasing the number of active devices in a RAID5 is much more
1445 effort. Every block in the array will need to be read and written
1446 back to a new location. From 2.6.17, the Linux Kernel is able to do
1447 this safely, including restart and interrupted "reshape".
1449 When relocating the first few stripes on a raid5, it is not possible
1450 to keep the data on disk completely consistent and crash-proof. To
1451 provide the required safety, mdadm disables writes to the array while
1452 this "critical section" is reshaped, and takes a backup of the data
1453 that is in that section. This backup is normally stored in any spare
1454 devices that the array has, however it can also be stored in a
1455 separate file specified with the
1457 option. If this option is used, and the system does crash during the
1458 critical period, the same file must be passed to
1460 to restore the backup and reassemble the array.
1464 A write-intent bitmap can be added to, or removed from, an active
1465 array. Either internal bitmaps, or bitmaps stored in a separate file
1466 can be added. Note that if you add a bitmap stored in a file which is
1467 in a filesystem that is on the raid array being affected, the system
1468 will deadlock. The bitmap must be on a separate filesystem.
1472 .B " mdadm --query /dev/name-of-device"
1474 This will find out if a given device is a raid array, or is part of
1475 one, and will provide brief information about the device.
1477 .B " mdadm --assemble --scan"
1479 This will assemble and start all arrays listed in the standard config file
1480 file. This command will typically go in a system startup file.
1482 .B " mdadm --stop --scan"
1484 This will shut down all array that can be shut down (i.e. are not
1485 currently in use). This will typically go in a system shutdown script.
1487 .B " mdadm --follow --scan --delay=120"
1489 If (and only if) there is an Email address or program given in the
1490 standard config file, then
1491 monitor the status of all arrays listed in that file by
1492 polling them ever 2 minutes.
1494 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1496 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1499 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1501 .B " mdadm --detail --scan >> mdadm.conf"
1503 This will create a prototype config file that describes currently
1504 active arrays that are known to be made from partitions of IDE or SCSI drives.
1505 This file should be reviewed before being used as it may
1506 contain unwanted detail.
1508 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1510 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1512 This will find what arrays could be assembled from existing IDE and
1513 SCSI whole drives (not partitions) and store the information is the
1514 format of a config file.
1515 This file is very likely to contain unwanted detail, particularly
1518 entries. It should be reviewed and edited before being used as an
1521 .B " mdadm --examine --brief --scan --config=partitions"
1523 .B " mdadm -Ebsc partitions"
1525 Create a list of devices by reading
1526 .BR /proc/partitions ,
1527 scan these for RAID superblocks, and printout a brief listing of all
1530 .B " mdadm -Ac partitions -m 0 /dev/md0"
1532 Scan all partitions and devices listed in
1533 .BR /proc/partitions
1536 out of all such devices with a RAID superblock with a minor number of 0.
1538 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1540 If config file contains a mail address or alert program, run mdadm in
1541 the background in monitor mode monitoring all md devices. Also write
1542 pid of mdadm daemon to
1543 .BR /var/run/mdadm .
1545 .B " mdadm --create --help"
1547 Provide help about the Create mode.
1549 .B " mdadm --config --help"
1551 Provide help about the format of the config file.
1555 Provide general help.
1566 lists all active md devices with information about them.
1568 uses this to find arrays when
1570 is given in Misc mode, and to monitor array reconstruction
1576 The config file lists which devices may be scanned to see if
1577 they contain MD super block, and gives identifying information
1578 (e.g. UUID) about known MD arrays. See
1584 While entries in the /dev directory can have any format you like,
1586 has an understanding of 'standard' formats which it uses to guide its
1587 behaviour when creating device files via the
1591 The standard names for non-partitioned arrays (the only sort of md
1592 array available in 2.4 and earlier) either of
1598 where NN is a number.
1599 The standard names for partitionable arrays (as available from 2.6
1606 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1610 was previously known as
1614 is completely separate from the
1616 package, and does not use the
1618 configuration file at all.
1621 For information on the various levels of
1625 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1626 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1629 '''for new releases of the RAID driver check out:
1632 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1633 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1638 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1639 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1642 The latest version of
1644 should always be available from
1646 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1647 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob