2 .TH MDADM 8 "" v2.4-pre1
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.
116 This is for doing things to specific components of an array such as
117 adding new spares and removing faulty devices.
121 This mode allows operations on independent devices such as examine MD
122 superblocks, erasing old superblocks and stopping active arrays.
125 .B "Follow or Monitor"
126 Monitor one or more md devices and act on any state changes. This is
127 only meaningful for raid1, 4, 5, 6, 10 or multipath arrays as
128 only these have interesting state. raid0 or linear never have
129 missing, spare, or failed drives, so there is nothing to monitor.
133 Grow (or shrink) an array, or otherwise reshape it in some way.
134 Currently supported growth options including changing the active size
135 of componenet devices in RAID level 1/4/5/6 and changing the number of
136 active devices in RAID1.
140 Available options are:
143 .BR -A ", " --assemble
144 Assemble a pre-existing array.
148 Build a legacy array without superblocks.
156 Examine a device to see
157 (1) if it is an md device and (2) if it is a component of an md
159 Information about what is discovered is presented.
163 Print detail of one or more md devices.
166 .BR -E ", " --examine
167 Print content of md superblock on device(s).
170 .BR -F ", " --follow ", " --monitor
177 Change the size or shape of an active array.
180 .BR -X ", " --examine-bitmap
181 Report information about a bitmap file.
185 Display general help message or, after one of the above options, a
186 mode specific help message.
190 Display more detailed help about command line parsing and some commonly
194 .BR -V ", " --version
195 Print version information for mdadm.
198 .BR -v ", " --verbose
199 Be more verbose about what is happening. This can be used twice to be
201 The extra verbosity currently only affects
204 .BR "--examine --scan" .
208 Avoid printing purely informative messages. With this,
210 will be silent unless there is something really important to report.
214 Be less verbose. This is used with
222 gives an intermediate level of verbosity.
225 .BR -W ", " --write-mostly
226 subsequent devices lists in a
231 command will be flagged as 'write-mostly'. This is valid for RAID1
232 only and means that the 'md' driver will avoid reading from these
233 devices if at all possible. This can be useful if mirroring over a
237 .BR -b ", " --bitmap=
238 Give the name of a bitmap file to use with this array. Can be used
239 with --create (file should not exist), --assemble (file should
240 exist), of --grow (file should not exist).
244 can be used to indicate that the bitmap should be stored in the array,
245 near the superblock. There is a limited amount of space for such
246 bitmaps, but it is often sufficient.
250 can be given when used with --grow to remove a bitmap.
252 To help catch typing errors, the filename must contain at least one
253 slash ('/') if it is a real file (not 'internal' or 'none').
255 Note: bitmaps are only known to work on ext2 and ext3. Using other
256 filesystems may result in serious problems.
260 Set the Chunksize of the bitmap. Each bit corresponds to that many
261 Kilobytes of storage. Default is 4.
265 Specify that write-behind mode should be enabled (valid for RAID1
266 only). If an argument is specified, it will set the maximum number
267 of outstanding writes allowed. The default value is 256.
268 A write-intent bitmap is required in order to use write-behind
269 mode, and write-behind is only attempted on drives marked as
275 Be more forceful about certain operations. See the various modes of
276 the exact meaning of this option in different contexts.
279 .BR -c ", " --config=
280 Specify the config file. Default is
281 .BR /etc/mdadm.conf .
282 If the config file given is
284 then nothing will be read, but
286 will act as though the config file contained exactly
287 .B "DEVICE partitions"
290 to find a list of devices to scan.
293 is given for the config file, then
295 will act as though the config file were empty.
301 for missing information.
302 In general, this option gives
304 permission to get any missing information, like component devices,
305 array devices, array identities, and alert destination from the
307 .BR /etc/mdadm.conf .
308 One exception is MISC mode when using
314 says to get a list of array devices from
318 .B -e ", " --metadata=
319 Declare the style of superblock (raid metadata) to be used. The
320 default is 0.90 for --create, and to guess for other operations.
324 .IP "0, 0.90, default"
325 Use the original 0.90 format superblock. This format limits arrays to
326 28 componenet devices and limits component devices of levels 1 and
327 greater to 2 terabytes.
328 .IP "1, 1.0, 1.1, 1.2"
329 Use the new version-1 format superblock. This has few restrictions.
330 The different subversion store the superblock at different locations
331 on the device, either at the end (for 1.0), at the start (for 1.1) or
332 4K from the start (for 1.2).
335 .SH For create or build:
339 Specify chunk size of kibibytes. The default is 64.
343 Specify rounding factor for linear array (==chunk size)
347 Set raid level. When used with
349 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
350 raid5, 5, raid6, 6, raid10, 10, multipath, mp, fautly. Obviously some of these are synonymous.
354 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
357 .BR -p ", " --layout=
358 This option configures the fine details of data layout for raid5,
359 and raid10 arrays, and controls the failure modes for
362 The layout of the raid5 parity block can be one of
367 la, ra, ls, rs. The default is left-symmetric.
369 When setting the failure mode for
387 Each mode can be followed by a number which is used as a period
388 between fault generation. Without a number, the fault is generated
389 once on the first relevant request. With a number, the fault will be
390 generated after that many request, and will continue to be generated
391 every time the period elapses.
393 Multiple failure modes can be current simultaneously by using the
394 "--grow" option to set subsequent failure modes.
396 "clear" or "none" will remove any pending or periodic failure modes,
397 and "flush" will clear any persistant faults.
399 To set the parity with "--grow", the level of the array ("faulty")
400 must be specified before the fault mode is specified.
402 Finally, the layout options for RAID10 are either 'n' or 'p' followed
403 by a small number. The default is 'n2'.
406 signals 'near' copies (multiple copies of one data block are at
407 similar offsets in different devices) while
410 (multiple copies have very different offsets). See md(4) for more
411 detail about 'near' and 'far'.
413 The number is the number of copies of each datablock. 2 is normal, 3
414 can be useful. This number can be at most equal to the number of
415 devices in the array. It does not need to divide evenly into that
416 number (e.g. it is perfectly legal to have an 'n2' layout for an array
417 with an odd number of devices).
421 same as --layout (thus explaining the p of
425 .BR -b ", " --bitmap=
426 Specify a file to store a write-intent bitmap in. The file should not
427 exist unless --force is also given. The same file should be provided
428 when assembling the array.
432 Specifty the chunksize for the bitmap.
435 .BR -n ", " --raid-devices=
436 Specify the number of active devices in the array. This, plus the
437 number of spare devices (see below) must equal the number of
439 (including "\fBmissing\fP" devices)
440 that are listed on the command line for
442 Setting a value of 1 is probably
443 a mistake and so requires that
445 be specified first. A value of 1 will then be allowed for linear,
446 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
448 This number can only be changed using
450 for RAID1 arrays, and only on kernels which provide necessary support.
453 .BR -x ", " --spare-devices=
454 Specify the number of spare (eXtra) devices in the initial array.
455 Spares can also be added
456 and removed later. The number of component devices listed
457 on the command line must equal the number of raid devices plus the
458 number of spare devices.
463 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
464 This must be a multiple of the chunk size, and must leave about 128Kb
465 of space at the end of the drive for the RAID superblock.
466 If this is not specified
467 (as it normally is not) the smallest drive (or partition) sets the
468 size, though if there is a variance among the drives of greater than 1%, a warning is
471 This value can be set with
473 for RAID level 1/4/5/6. If the array was created with a size smaller
474 than the currently active drives, the extra space can be accessed
477 The size can be given as
479 which means to choose the largest size that fits on all current drives.
485 that the array pre-existed and is known to be clean. It can be useful
486 when trying to recover from a major failure as you can be sure that no
487 data will be affected unless you actually write to the array. It can
488 also be used when creating a RAID1 or RAID10 if you want to avoid the
489 initial resync, however this practice - while normally safe - is not
490 recommended. Use this ony if you really know what you are doing.
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 haveo
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.
614 .BR -U ", " --update=
615 Update the superblock on each device while assembling the array. The
616 argument given to this flag can be one of
627 option will adjust the superblock of an array what was created on a Sparc
628 machine running a patched 2.2 Linux kernel. This kernel got the
629 alignment of part of the superblock wrong. You can use the
630 .B "--examine --sparc2.2"
633 to see what effect this would have.
637 option will update the
639 field on each superblock to match the minor number of the array being
640 assembled. This is not needed on 2.6 and later kernels as they make
641 this adjustment automatically.
645 option will change the uuid of the array. If a UUID is given with the
646 "--uuid" option that UUID will be used as a new UUID and with
648 be used to help identify the devices in the array.
649 If no "--uuid" is given, a random uuid is chosen.
653 option will cause the array to be marked
655 meaning that any redundancy in the array (e.g. parity for raid5,
656 copies for raid1) may be incorrect. This will cause the raid system
657 to perform a "resync" pass to make sure that all redundant information
662 option allows arrays to be moved between machines with different
664 When assembling such an array for the first time after a move, giving
665 .B "--update=byteorder"
668 to expect superblocks to have their byteorder reversed, and will
669 correct that order before assembling the array. This is only valid
670 with original (Verion 0.90) superblocks.
674 option will correct the summaries in the superblock. That is the
675 counts of total, working, active, failed, and spare devices.
682 hotadd listed devices.
686 Listed devices are assumed to have recently been part of the array,
687 and they are re-added. This is only different from --add when a
688 write-intent bitmap is present. It causes only those parts of the
689 device that have changed since the device was removed from the array
692 This flag is only needed with arrays that are built without a
693 superblock (i.e. --build, not --create). For array with a superblock,
695 checks if a superblock is present and automatically determines if a
696 re-add is appropriate.
700 remove listed devices. They must not be active. i.e. they should
701 be failed or spare devices.
705 mark listed devices as faulty.
711 .SH For Examine mode:
715 If an array was created on a 2.2 Linux kernel patched with RAID
716 support, the superblock will have been created incorrectly, or at
717 least incompatibly with 2.4 and later kernels. Using the
721 will fix the superblock before displaying it. If this appears to do
722 the right thing, then the array can be successfully assembled using
723 .BR "--assemble --update=sparc2.2" .
729 start a partially built array.
733 deactivate array, releasing all resources.
736 .BR -o ", " --readonly
737 mark array as readonly.
740 .BR -w ", " --readwrite
741 mark array as readwrite.
745 If the device contains a valid md superblock, the block is
746 over-written with zeros. With
748 the block where the superblock would be is over-written even if it
749 doesn't appear to be valid.
757 is set to reflect the status of the device.
759 .SH For Monitor mode:
762 Give a mail address to send alerts to.
765 .BR -p ", " --program ", " --alert
766 Give a program to be run whenever an event is detected.
770 Cause all events to be reported through 'syslog'. The messages have
771 facility of 'daemon' and varying priorities.
775 Give a delay in seconds.
777 polls the md arrays and then waits this many seconds before polling
778 again. The default is 60 seconds.
781 .BR -f ", " --daemonise
784 to run as a background daemon if it decides to monitor anything. This
785 causes it to fork and run in the child, and to disconnect form the
786 terminal. The process id of the child is written to stdout.
789 which will only continue monitoring if a mail address or alert program
790 is found in the config file.
793 .BR -i ", " --pid-file
796 is running in daemon mode, write the pid of the daemon process to
797 the specified file, instead of printing it on standard output.
800 .BR -1 ", " --oneshot
801 Check arrays only once. This will generate
803 events and more significantly
809 .B " mdadm --monitor --scan -1"
811 from a cron script will ensure regular notification of any degraded arrays.
817 alert for every array found at startup. This alert gets mailed and
818 passed to the alert program. This can be used for testing that alert
819 message do get through successfully.
826 .I md-device options-and-component-devices...
829 .B mdadm --assemble --scan
830 .I md-devices-and-options...
833 .B mdadm --assemble --scan
837 This usage assembles one or more raid arrays from pre-existing components.
838 For each array, mdadm needs to know the md device, the identity of the
839 array, and a number of component-devices. These can be found in a number of ways.
841 In the first usage example (without the
843 the first device given is the md device.
844 In the second usage example, all devices listed are treated as md
845 devices and assembly is attempted.
846 In the third (where no devices are listed) all md devices that are
847 listed in the configuration file are assembled.
849 If precisely one device is listed, but
855 was given and identify information is extracted from the configuration file.
857 The identity can be given with the
861 option, can be found in the config file, or will be taken from the
862 super block on the first component-device listed on the command line.
864 Devices can be given on the
866 command line or in the config file. Only devices which have an md
867 superblock which contains the right identity will be considered for
870 The config file is only used if explicitly named with
872 or requested with (a possibly implicit)
880 is not given, then the config file will only be used to find the
881 identity of md arrays.
883 Normally the array will be started after it is assembled. However if
885 is not given and insufficient drives were listed to start a complete
886 (non-degraded) array, then the array is not started (to guard against
887 usage errors). To insist that the array be started in this case (as
888 may work for RAID1, 4, 5, 6, or 10), give the
894 option is given, either on the command line (--auto) or in the
895 configuration file (e.g. auto=part), then
897 will create the md device if necessary or will re-create it if it
898 doesn't look usable as it is.
900 This can be useful for handling partitioned devices (which don't have
901 a stable device number - it can change after a reboot) and when using
902 "udev" to manage your
904 tree (udev cannot handle md devices because of the unusual device
905 initialisation conventions).
907 If the option to "auto" is "mdp" or "part" or (on the command line
908 only) "p", then mdadm will create a partitionable array, using the
909 first free one that is not inuse, and does not already have an entry
910 in /dev (apart from numeric /dev/md* entries).
912 If the option to "auto" is "yes" or "md" or (on the command line)
913 nothing, then mdadm will create a traditional, non-partitionable md
916 It is expected that the "auto" functionality will be used to create
917 device entries with meaningful names such as "/dev/md/home" or
918 "/dev/md/root", rather than names based on the numerical array number.
920 When using this option to create a partitionable array, the device
921 files for the first 4 partitions are also created. If a different
922 number is required it can be simply appended to the auto option.
923 e.g. "auto=part8". Partition names are created by appending a digit
924 string to the device name, with an intervening "p" if the device name
929 option is also available in Build and Create modes. As those modes do
930 not use a config file, the "auto=" config option does not apply to
941 .BI --raid-devices= Z
945 This usage is similar to
947 The difference is that it creates an array without a superblock. With
948 these arrays there is no difference between initially creating the array and
949 subsequently assembling the array, except that hopefully there is useful
950 data there in the second case.
952 The level may raid0, linear, multipath, or faulty, or one of their
953 synonyms. All devices must be listed and the array will be started
965 .BI --raid-devices= Z
969 This usage will initialise a new md array, associate some devices with
970 it, and activate the array.
974 option is given (as described in more detail in the section on
975 Assemble mode), then the md device will be created with a suitable
976 device number if necessary.
978 As devices are added, they are checked to see if they contain raid
979 superblocks or filesystems. They are also checked to see if the variance in
980 device size exceeds 1%.
982 If any discrepancy is found, the array will not automatically be run, though
985 can override this caution.
987 To create a "degraded" array in which some devices are missing, simply
988 give the word "\fBmissing\fP"
989 in place of a device name. This will cause
991 to leave the corresponding slot in the array empty.
992 For a RAID4 or RAID5 array at most one slot can be
993 "\fBmissing\fP"; for a RAID6 array at most two slots.
994 For a RAID1 array, only one real device needs to be given. All of the
998 When creating a RAID5 array,
1000 will automatically create a degraded array with an extra spare drive.
1001 This is because building the spare into a degraded array is in general faster than resyncing
1002 the parity on a non-degraded, but not clean, array. This feature can
1003 be over-ridden with the
1009 '''option is given, it is not necessary to list any component-devices in this command.
1010 '''They can be added later, before a
1014 '''is given, the apparent size of the smallest drive given is used.
1016 The General Management options that are valid with --create are:
1019 insist on running the array even if some devices look like they might
1024 start the array readonly - not supported yet.
1031 .I options... devices...
1034 This usage will allow individual devices in an array to be failed,
1035 removed or added. It is possible to perform multiple operations with
1036 on command. For example:
1038 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1044 and will then remove it from the array and finally add it back
1045 in as a spare. However only one md array can be affected by a single
1056 MISC mode includes a number of distinct operations that
1057 operate on distinct devices. The operations are:
1060 The device is examined to see if it is
1061 (1) an active md array, or
1062 (2) a component of an md array.
1063 The information discovered is reported.
1067 The device should be an active md device.
1069 will display a detailed description of the array.
1073 will cause the output to be less detailed and the format to be
1074 suitable for inclusion in
1075 .BR /etc/mdadm.conf .
1078 will normally be 0 unless
1080 failed to get useful information about the device(s). However if the
1082 option is given, then the exit status will be:
1086 The array is functioning normally.
1089 The array has at least one failed device.
1092 The array has multiple failed devices and hence is unusable (raid4 or
1096 There was an error while trying to get information about the device.
1101 The device should be a component of an md array.
1103 will read the md superblock of the device and display the contents.
1108 then multiple devices that are components of the one array
1109 are grouped together and reported in a single entry suitable
1111 .BR /etc/mdadm.conf .
1115 without listing any devices will cause all devices listed in the
1116 config file to be examined.
1120 The devices should be active md arrays which will be deactivated, as
1121 long as they are not currently in use.
1125 This will fully activate a partially assembled md array.
1129 This will mark an active array as read-only, providing that it is
1130 not currently being used.
1136 array back to being read/write.
1140 For all operations except
1143 will cause the operation to be applied to all arrays listed in
1148 causes all devices listed in the config file to be examined.
1156 .I options... devices...
1161 to periodically poll a number of md arrays and to report on any events
1164 will never exit once it decides that there are arrays to be checked,
1165 so it should normally be run in the background.
1167 As well as reporting events,
1169 may move a spare drive from one array to another if they are in the
1172 and if the destination array has a failed drive but no spares.
1174 If any devices are listed on the command line,
1176 will only monitor those devices. Otherwise all arrays listed in the
1177 configuration file will be monitored. Further, if
1179 is given, then any other md devices that appear in
1181 will also be monitored.
1183 The result of monitoring the arrays is the generation of events.
1184 These events are passed to a separate program (if specified) and may
1185 be mailed to a given E-mail address.
1187 When passing event to program, the program is run once for each event
1188 and is given 2 or 3 command-line arguements. The first is the
1189 name of the event (see below). The second is the name of the
1190 md device which is affected, and the third is the name of a related
1191 device if relevant, such as a component device that has failed.
1195 is given, then a program or an E-mail address must be specified on the
1196 command line or in the config file. If neither are available, then
1198 will not monitor anything.
1202 will continue monitoring as long as something was found to monitor. If
1203 no program or email is given, then each event is reported to
1206 The different events are:
1210 .B DeviceDisappeared
1211 An md array which previously was configured appears to no longer be
1212 configured. (syslog priority: Critical)
1216 was told to monitor an array which is RAID0 or Linear, then it will
1218 .B DeviceDisappeared
1219 with the extra information
1221 This is because RAID0 and Linear do not support the device-failed,
1222 hot-spare and resync operations which are monitored.
1226 An md array started reconstruction. (syslog priority: Warning)
1232 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1233 percentage of the total. (syslog priority: Warning)
1237 An md array that was rebuilding, isn't any more, either because it
1238 finished normally or was aborted. (syslog priority: Warning)
1242 An active component device of an array has been marked as
1243 faulty. (syslog priority: Critical)
1247 A spare component device which was being rebuilt to replace a faulty
1248 device has failed. (syslog priority: Critial)
1252 A spare component device which was being rebuilt to replace a faulty
1253 device as been successfully rebuild and has been made active.
1254 (syslog priority: Info)
1258 A new md array has been detected in the
1260 file. (syslog priority: Info)
1264 A newly noticed array appears to be degraded. This message is not
1267 notices a drive failure which causes degradation, but only when
1269 notices that an array is degraded when it first sees the array.
1270 (syslog priority: Critial)
1274 A spare drive has been moved from one array in a
1276 to another to allow a failed drive to be replaced.
1277 (syslog priority: Info)
1283 has been told, via the config file, that an array should have a certain
1284 number of spare devices, and
1286 detects that it has fewer that this number when it first sees the
1287 array, it will report a
1290 (syslog priority: Info)
1294 An array was found at startup, and the
1297 (syslog priority: Info)
1306 cause Email to be sent. All events cause the program to be run.
1307 The program is run with two or three arguments, they being the event
1308 name, the array device and possibly a second device.
1310 Each event has an associated array device (e.g.
1312 and possibly a second device. For
1317 the second device is the relevant component device.
1320 the second device is the array that the spare was moved from.
1324 to move spares from one array to another, the different arrays need to
1325 be labelled with the same
1327 in the configuration file. The
1329 name can be any string. It is only necessary that different spare
1330 groups use different names.
1334 detects that an array which is in a spare group has fewer active
1335 devices than necessary for the complete array, and has no spare
1336 devices, it will look for another array in the same spare group that
1337 has a full complement of working drive and a spare. It will then
1338 attempt to remove the spare from the second drive and add it to the
1340 If the removal succeeds but the adding fails, then it is added back to
1344 The GROW mode is used for changing the size or shape of an active
1346 For this to work, the kernel must support the necessary change.
1347 Various types of growth may be added during 2.6 development, possibly
1348 including restructuring a raid5 array to have more active devices.
1350 Currently the only support available is to
1352 change the "size" attribute
1353 for RAID1, RAID5 and RAID6.
1355 change the "raid-disks" attribute of RAID1.
1357 add a write-intent bitmap to a RAID1 array.
1360 Normally when an array is built the "size" it taken from the smallest
1361 of the drives. If all the small drives in an arrays are, one at a
1362 time, removed and replaced with larger drives, then you could have an
1363 array of large drives with only a small amount used. In this
1364 situation, changing the "size" with "GROW" mode will allow the extra
1365 space to start being used. If the size is increased in this way, a
1366 "resync" process will start to make sure the new parts of the array
1369 Note that when an array changes size, any filesystem that may be
1370 stored in the array will not automatically grow to use the space. The
1371 filesystem will need to be explicitly told to use the extra space.
1373 A RAID1 array can work with any number of devices from 1 upwards
1374 (though 1 is not very useful). There may be times which you want to
1375 increase or decrease the number of active devices. Note that this is
1376 different to hot-add or hot-remove which changes the number of
1379 When reducing the number of devices in a RAID1 array, the slots which
1380 are to be removed from the array must already be vacant. That is, the
1381 devices that which were in those slots must be failed and removed.
1383 When the number of devices is increased, any hot spares that are
1384 present will be activated immediately.
1386 A write-intent bitmap can be added to, or remove from, an active RAID1
1387 array. Either internal bitmap, of bitmaps stored in a separate file
1388 can be added. Note that if you add a bitmap stored in a file which is
1389 in a filesystem that is on the raid array being affected, the system
1390 will deadlock. The bitmap must be on a separate filesystem.
1394 .B " mdadm --query /dev/name-of-device"
1396 This will find out if a given device is a raid array, or is part of
1397 one, and will provide brief information about the device.
1399 .B " mdadm --assemble --scan"
1401 This will assemble and start all arrays listed in the standard confile
1402 file. This command will typically go in a system startup file.
1404 .B " mdadm --stop --scan"
1406 This will shut down all array that can be shut down (i.e. are not
1407 currently in use). This will typically go in a system shutdown script.
1409 .B " mdadm --follow --scan --delay=120"
1411 If (and only if) there is an Email address or program given in the
1412 standard config file, then
1413 monitor the status of all arrays listed in that file by
1414 polling them ever 2 minutes.
1416 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1418 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1421 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1423 .B " mdadm --detail --scan >> mdadm.conf"
1425 This will create a prototype config file that describes currently
1426 active arrays that are known to be made from partitions of IDE or SCSI drives.
1427 This file should be reviewed before being used as it may
1428 contain unwanted detail.
1430 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1432 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1434 This will find what arrays could be assembled from existign IDE and
1435 SCSI whole drives (not partitions) and store the information is the
1436 format of a config file.
1437 This file is very likely to contain unwanted detail, particularly
1440 entries. It should be reviewed and edited before being used as an
1443 .B " mdadm --examine --brief --scan --config=partitions"
1445 .B " mdadm -Ebsc partitions"
1447 Create a list of devices by reading
1448 .BR /proc/partitions ,
1449 scan these for RAID superblocks, and printout a brief listing of all
1452 .B " mdadm -Ac partitions -m 0 /dev/md0"
1454 Scan all partitions and devices listed in
1455 .BR /proc/partitions
1458 out of all such devices with a RAID superblock with a minor number of 0.
1460 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1462 If config file contains a mail address or alert program, run mdadm in
1463 the background in monitor mode monitoring all md devices. Also write
1464 pid of mdadm daemon to
1465 .BR /var/run/mdadm .
1467 .B " mdadm --create --help"
1469 Providew help about the Create mode.
1471 .B " mdadm --config --help"
1473 Provide help about the format of the config file.
1477 Provide general help.
1488 lists all active md devices with information about them.
1490 uses this to find arrays when
1492 is given in Misc mode, and to monitor array reconstruction
1498 The config file lists which devices may be scanned to see if
1499 they contain MD super block, and gives identifying information
1500 (e.g. UUID) about known MD arrays. See
1506 While entries in the /dev directory can have any format you like,
1508 has an understanding of 'standard' formats which it uses to guide its
1509 behaviour when creating device files via the
1513 The standard names for non-partitioned arrays (the only sort of md
1514 array available in 2.4 and earlier) either of
1520 where NN is a number.
1521 The standard names for partitionable arrays (as available from 2.6
1528 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1532 was previously known as
1536 is completely separate from the
1538 package, and does not use the
1540 configuration file at all.
1543 For information on the various levels of
1547 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1548 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1551 '''for new releases of the RAID driver check out:
1554 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1555 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1560 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1561 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1564 The lastest version of
1566 should always be available from
1568 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1569 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob