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.
254 Set the Chunksize of the bitmap. Each bit corresponds to that many
255 Kilobytes of storage. Default is 4.
259 Specify that write-behind mode should be enabled (valid for RAID1
260 only). If an argument is specified, it will set the maximum number
261 of outstanding writes allowed. The default value is 256.
262 A write-intent bitmap is required in order to use write-behind
263 mode, and write-behind is only attempted on drives marked as
269 Be more forceful about certain operations. See the various modes of
270 the exact meaning of this option in different contexts.
273 .BR -c ", " --config=
274 Specify the config file. Default is
275 .BR /etc/mdadm.conf .
276 If the config file given is
278 then nothing will be read, but
280 will act as though the config file contained exactly
281 .B "DEVICE partitions"
284 to find a list of devices to scan.
287 is given for the config file, then
289 will act as though the config file were empty.
295 for missing information.
296 In general, this option gives
298 permission to get any missing information, like component devices,
299 array devices, array identities, and alert destination from the
301 .BR /etc/mdadm.conf .
302 One exception is MISC mode when using
308 says to get a list of array devices from
312 .B -e ", " --metadata=
313 Declare the style of superblock (raid metadata) to be used. The
314 default is 0.90 for --create, and to guess for other operations.
318 .IP "0, 0.90, default"
319 Use the original 0.90 format superblock. This format limits arrays to
320 28 componenet devices and limits component devices of levels 1 and
321 greater to 2 terabytes.
322 .IP "1, 1.0, 1.1, 1.2"
323 Use the new version-1 format superblock. This has few restrictions.
324 The different subversion store the superblock at different locations
325 on the device, either at the end (for 1.0), at the start (for 1.1) or
326 4K from the start (for 1.2).
329 .SH For create or build:
333 Specify chunk size of kibibytes. The default is 64.
337 Specify rounding factor for linear array (==chunk size)
341 Set raid level. When used with
343 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
344 raid5, 5, raid6, 6, raid10, 10, multipath, mp, fautly. Obviously some of these are synonymous.
348 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
351 .BR -p ", " --layout=
352 This option configures the fine details of data layout for raid5,
353 and raid10 arrays, and controls the failure modes for
356 The layout of the raid5 parity block can be one of
361 la, ra, ls, rs. The default is left-symmetric.
363 When setting the failure mode for
381 Each mode can be followed by a number which is used as a period
382 between fault generation. Without a number, the fault is generated
383 once on the first relevant request. With a number, the fault will be
384 generated after that many request, and will continue to be generated
385 every time the period elapses.
387 Multiple failure modes can be current simultaneously by using the
388 "--grow" option to set subsequent failure modes.
390 "clear" or "none" will remove any pending or periodic failure modes,
391 and "flush" will clear any persistant faults.
393 To set the parity with "--grow", the level of the array ("faulty")
394 must be specified before the fault mode is specified.
396 Finally, the layout options for RAID10 are either 'n' or 'p' followed
397 by a small number. The default is 'n2'.
400 signals 'near' copies (multiple copies of one data block are at
401 similar offsets in different devices) while
404 (multiple copies have very different offsets). See md(4) for more
405 detail about 'near' and 'far'.
407 The number is the number of copies of each datablock. 2 is normal, 3
408 can be useful. This number can be at most equal to the number of
409 devices in the array. It does not need to divide evenly into that
410 number (e.g. it is perfectly legal to have an 'n2' layout for an array
411 with an odd number of devices).
415 same as --layout (thus explaining the p of
419 .BR -b ", " --bitmap=
420 Specify a file to store a write-intent bitmap in. The file should not
421 exist unless --force is also given. The same file should be provided
422 when assembling the array.
426 Specifty the chunksize for the bitmap.
429 .BR -n ", " --raid-devices=
430 Specify the number of active devices in the array. This, plus the
431 number of spare devices (see below) must equal the number of
433 (including "\fBmissing\fP" devices)
434 that are listed on the command line for
436 Setting a value of 1 is probably
437 a mistake and so requires that
439 be specified first. A value of 1 will then be allowed for linear,
440 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
442 This number can only be changed using
444 for RAID1 arrays, and only on kernels which provide necessary support.
447 .BR -x ", " --spare-devices=
448 Specify the number of spare (eXtra) devices in the initial array.
449 Spares can also be added
450 and removed later. The number of component devices listed
451 on the command line must equal the number of raid devices plus the
452 number of spare devices.
457 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
458 This must be a multiple of the chunk size, and must leave about 128Kb
459 of space at the end of the drive for the RAID superblock.
460 If this is not specified
461 (as it normally is not) the smallest drive (or partition) sets the
462 size, though if there is a variance among the drives of greater than 1%, a warning is
465 This value can be set with
467 for RAID level 1/4/5/6. If the array was created with a size smaller
468 than the currently active drives, the extra space can be accessed
471 The size can be given as
473 which means to choose the largest size that fits on all current drives.
479 that the array pre-existed and is known to be clean. It can be useful
480 when trying to recover from a major failure as you can be sure that no
481 data will be affected unless you actually write to the array. It can
482 also be used when creating a RAID1 or RAID10 if you want to avoid the
483 initial resync, however this practice - while normally safe - is not
484 recommended. Use this ony if you really know what you are doing.
490 for the array. This is currently only effective when creating an
491 array with a version-1 superblock. The name is a simple textual
492 string that can be used to identify array components when assembling.
498 run the array, even if some of the components
499 appear to be active in another array or filesystem. Normally
501 will ask for confirmation before including such components in an
502 array. This option causes that question to be suppressed.
508 accept the geometry and layout specified without question. Normally
510 will not allow creation of an array with only one device, and will try
511 to create a raid5 array with one missing drive (as this makes the
512 initial resync work faster). With
515 will not try to be so clever.
518 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
519 Instruct mdadm to create the device file if needed, possibly allocating
520 an unused minor number. "md" causes a non-partitionable array
521 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
522 later) to be used. "yes" requires the named md device to haveo
523 a 'standard' format, and the type and minor number will be determined
524 from this. See DEVICE NAMES below.
526 The argument can also come immediately after
531 is also given, then any
533 entries in the config file will over-ride the
535 instruction given on the command line.
537 For partitionable arrays,
539 will create the device file for the whole array and for the first 4
540 partitions. A different number of partitions can be specified at the
541 end of this option (e.g.
543 If the device name ends with a digit, the partition names add a'p',
544 and a number, e.g. "/dev/home1p3". If there is no
545 trailing digit, then the partition names just have a number added,
546 e.g. "/dev/scratch3".
548 If the md device name is in a 'standard' format as described in DEVICE
549 NAMES, then it will be created, if necessary, with the appropriate
550 number based on that name. If the device name is not in one of these
551 formats, then a unused minor number will be allocated. The minor
552 number will be considered unused if there is no active array for that
553 number, and there is no entry in /dev for that number and with a
560 uuid of array to assemble. Devices which don't have this uuid are
564 .BR -m ", " --super-minor=
565 Minor number of device that array was created for. Devices which
566 don't have this minor number are excluded. If you create an array as
567 /dev/md1, then all superblocks will contain the minor number 1, even if
568 the array is later assembled as /dev/md2.
570 Giving the literal word "dev" for
574 to use the minor number of the md device that is being assembled.
578 will look for super blocks with a minor number of 0.
582 Specify the name of the array to assemble. This must be the name
583 that was specified when creating the array.
587 Assemble the array even if some superblocks appear out-of-date
591 Attempt to start the array even if fewer drives were given than are
592 needed for a full array. Normally if not all drives are found and
594 is not used, then the array will be assembled but not started.
597 an attempt will be made to start it anyway.
600 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
601 See this option under Create and Build options.
604 .BR -b ", " --bitmap=
605 Specify the bitmap file that was given when the array was created.
608 .BR -U ", " --update=
609 Update the superblock on each device while assembling the array. The
610 argument given to this flag can be one of
621 option will adjust the superblock of an array what was created on a Sparc
622 machine running a patched 2.2 Linux kernel. This kernel got the
623 alignment of part of the superblock wrong. You can use the
624 .B "--examine --sparc2.2"
627 to see what effect this would have.
631 option will update the
633 field on each superblock to match the minor number of the array being
634 assembled. This is not needed on 2.6 and later kernels as they make
635 this adjustment automatically.
639 option will change the uuid of the array. If a UUID is given with the
640 "--uuid" option that UUID will be used as a new UUID and with
642 be used to help identify the devices in the array.
643 If no "--uuid" is given, a random uuid is chosen.
647 option will cause the array to be marked
649 meaning that any redundancy in the array (e.g. parity for raid5,
650 copies for raid1) may be incorrect. This will cause the raid system
651 to perform a "resync" pass to make sure that all redundant information
656 option allows arrays to be moved between machines with different
658 When assembling such an array for the first time after a move, giving
659 .B "--update=byteorder"
662 to expect superblocks to have their byteorder reversed, and will
663 correct that order before assembling the array. This is only valid
664 with original (Verion 0.90) superblocks.
668 option will correct the summaries in the superblock. That is the
669 counts of total, working, active, failed, and spare devices.
676 hotadd listed devices.
680 Listed devices are assumed to have recently been part of the array,
681 and they are re-added. This is only different from --add when a
682 write-intent bitmap is present. It causes only those parts of the
683 device that have changed since the device was removed from the array
686 This flag is only needed with arrays that are built without a
687 superblock (i.e. --build, not --create). For array with a superblock,
689 checks if a superblock is present and automatically determines if a
690 re-add is appropriate.
694 remove listed devices. They must not be active. i.e. they should
695 be failed or spare devices.
699 mark listed devices as faulty.
705 .SH For Examine mode:
709 If an array was created on a 2.2 Linux kernel patched with RAID
710 support, the superblock will have been created incorrectly, or at
711 least incompatibly with 2.4 and later kernels. Using the
715 will fix the superblock before displaying it. If this appears to do
716 the right thing, then the array can be successfully assembled using
717 .BR "--assemble --update=sparc2.2" .
723 start a partially built array.
727 deactivate array, releasing all resources.
730 .BR -o ", " --readonly
731 mark array as readonly.
734 .BR -w ", " --readwrite
735 mark array as readwrite.
739 If the device contains a valid md superblock, the block is
740 over-written with zeros. With
742 the block where the superblock would be is over-written even if it
743 doesn't appear to be valid.
751 is set to reflect the status of the device.
753 .SH For Monitor mode:
756 Give a mail address to send alerts to.
759 .BR -p ", " --program ", " --alert
760 Give a program to be run whenever an event is detected.
764 Cause all events to be reported through 'syslog'. The messages have
765 facility of 'daemon' and varying priorities.
769 Give a delay in seconds.
771 polls the md arrays and then waits this many seconds before polling
772 again. The default is 60 seconds.
775 .BR -f ", " --daemonise
778 to run as a background daemon if it decides to monitor anything. This
779 causes it to fork and run in the child, and to disconnect form the
780 terminal. The process id of the child is written to stdout.
783 which will only continue monitoring if a mail address or alert program
784 is found in the config file.
787 .BR -i ", " --pid-file
790 is running in daemon mode, write the pid of the daemon process to
791 the specified file, instead of printing it on standard output.
794 .BR -1 ", " --oneshot
795 Check arrays only once. This will generate
797 events and more significantly
803 .B " mdadm --monitor --scan -1"
805 from a cron script will ensure regular notification of any degraded arrays.
811 alert for every array found at startup. This alert gets mailed and
812 passed to the alert program. This can be used for testing that alert
813 message do get through successfully.
820 .I md-device options-and-component-devices...
823 .B mdadm --assemble --scan
824 .I md-devices-and-options...
827 .B mdadm --assemble --scan
831 This usage assembles one or more raid arrays from pre-existing components.
832 For each array, mdadm needs to know the md device, the identity of the
833 array, and a number of component-devices. These can be found in a number of ways.
835 In the first usage example (without the
837 the first device given is the md device.
838 In the second usage example, all devices listed are treated as md
839 devices and assembly is attempted.
840 In the third (where no devices are listed) all md devices that are
841 listed in the configuration file are assembled.
843 If precisely one device is listed, but
849 was given and identify information is extracted from the configuration file.
851 The identity can be given with the
855 option, can be found in the config file, or will be taken from the
856 super block on the first component-device listed on the command line.
858 Devices can be given on the
860 command line or in the config file. Only devices which have an md
861 superblock which contains the right identity will be considered for
864 The config file is only used if explicitly named with
866 or requested with (a possibly implicit)
874 is not given, then the config file will only be used to find the
875 identity of md arrays.
877 Normally the array will be started after it is assembled. However if
879 is not given and insufficient drives were listed to start a complete
880 (non-degraded) array, then the array is not started (to guard against
881 usage errors). To insist that the array be started in this case (as
882 may work for RAID1, 4, 5, 6, or 10), give the
888 option is given, either on the command line (--auto) or in the
889 configuration file (e.g. auto=part), then
891 will create the md device if necessary or will re-create it if it
892 doesn't look usable as it is.
894 This can be useful for handling partitioned devices (which don't have
895 a stable device number - it can change after a reboot) and when using
896 "udev" to manage your
898 tree (udev cannot handle md devices because of the unusual device
899 initialisation conventions).
901 If the option to "auto" is "mdp" or "part" or (on the command line
902 only) "p", then mdadm will create a partitionable array, using the
903 first free one that is not inuse, and does not already have an entry
904 in /dev (apart from numeric /dev/md* entries).
906 If the option to "auto" is "yes" or "md" or (on the command line)
907 nothing, then mdadm will create a traditional, non-partitionable md
910 It is expected that the "auto" functionality will be used to create
911 device entries with meaningful names such as "/dev/md/home" or
912 "/dev/md/root", rather than names based on the numerical array number.
914 When using this option to create a partitionable array, the device
915 files for the first 4 partitions are also created. If a different
916 number is required it can be simply appended to the auto option.
917 e.g. "auto=part8". Partition names are created by appending a digit
918 string to the device name, with an intervening "p" if the device name
923 option is also available in Build and Create modes. As those modes do
924 not use a config file, the "auto=" config option does not apply to
935 .BI --raid-devices= Z
939 This usage is similar to
941 The difference is that it creates an array without a superblock. With
942 these arrays there is no difference between initially creating the array and
943 subsequently assembling the array, except that hopefully there is useful
944 data there in the second case.
946 The level may raid0, linear, multipath, or faulty, or one of their
947 synonyms. All devices must be listed and the array will be started
959 .BI --raid-devices= Z
963 This usage will initialise a new md array, associate some devices with
964 it, and activate the array.
968 option is given (as described in more detail in the section on
969 Assemble mode), then the md device will be created with a suitable
970 device number if necessary.
972 As devices are added, they are checked to see if they contain raid
973 superblocks or filesystems. They are also checked to see if the variance in
974 device size exceeds 1%.
976 If any discrepancy is found, the array will not automatically be run, though
979 can override this caution.
981 To create a "degraded" array in which some devices are missing, simply
982 give the word "\fBmissing\fP"
983 in place of a device name. This will cause
985 to leave the corresponding slot in the array empty.
986 For a RAID4 or RAID5 array at most one slot can be
987 "\fBmissing\fP"; for a RAID6 array at most two slots.
988 For a RAID1 array, only one real device needs to be given. All of the
992 When creating a RAID5 array,
994 will automatically create a degraded array with an extra spare drive.
995 This is because building the spare into a degraded array is in general faster than resyncing
996 the parity on a non-degraded, but not clean, array. This feature can
997 be over-ridden with the
1003 '''option is given, it is not necessary to list any component-devices in this command.
1004 '''They can be added later, before a
1008 '''is given, the apparent size of the smallest drive given is used.
1010 The General Management options that are valid with --create are:
1013 insist on running the array even if some devices look like they might
1018 start the array readonly - not supported yet.
1025 .I options... devices...
1028 This usage will allow individual devices in an array to be failed,
1029 removed or added. It is possible to perform multiple operations with
1030 on command. For example:
1032 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1038 and will then remove it from the array and finally add it back
1039 in as a spare. However only one md array can be affected by a single
1050 MISC mode includes a number of distinct operations that
1051 operate on distinct devices. The operations are:
1054 The device is examined to see if it is
1055 (1) an active md array, or
1056 (2) a component of an md array.
1057 The information discovered is reported.
1061 The device should be an active md device.
1063 will display a detailed description of the array.
1067 will cause the output to be less detailed and the format to be
1068 suitable for inclusion in
1069 .BR /etc/mdadm.conf .
1072 will normally be 0 unless
1074 failed to get useful information about the device(s). However if the
1076 option is given, then the exit status will be:
1080 The array is functioning normally.
1083 The array has at least one failed device.
1086 The array has multiple failed devices and hence is unusable (raid4 or
1090 There was an error while trying to get information about the device.
1095 The device should be a component of an md array.
1097 will read the md superblock of the device and display the contents.
1102 then multiple devices that are components of the one array
1103 are grouped together and reported in a single entry suitable
1105 .BR /etc/mdadm.conf .
1109 without listing any devices will cause all devices listed in the
1110 config file to be examined.
1114 The devices should be active md arrays which will be deactivated, as
1115 long as they are not currently in use.
1119 This will fully activate a partially assembled md array.
1123 This will mark an active array as read-only, providing that it is
1124 not currently being used.
1130 array back to being read/write.
1134 For all operations except
1137 will cause the operation to be applied to all arrays listed in
1142 causes all devices listed in the config file to be examined.
1150 .I options... devices...
1155 to periodically poll a number of md arrays and to report on any events
1158 will never exit once it decides that there are arrays to be checked,
1159 so it should normally be run in the background.
1161 As well as reporting events,
1163 may move a spare drive from one array to another if they are in the
1166 and if the destination array has a failed drive but no spares.
1168 If any devices are listed on the command line,
1170 will only monitor those devices. Otherwise all arrays listed in the
1171 configuration file will be monitored. Further, if
1173 is given, then any other md devices that appear in
1175 will also be monitored.
1177 The result of monitoring the arrays is the generation of events.
1178 These events are passed to a separate program (if specified) and may
1179 be mailed to a given E-mail address.
1181 When passing event to program, the program is run once for each event
1182 and is given 2 or 3 command-line arguements. The first is the
1183 name of the event (see below). The second is the name of the
1184 md device which is affected, and the third is the name of a related
1185 device if relevant, such as a component device that has failed.
1189 is given, then a program or an E-mail address must be specified on the
1190 command line or in the config file. If neither are available, then
1192 will not monitor anything.
1196 will continue monitoring as long as something was found to monitor. If
1197 no program or email is given, then each event is reported to
1200 The different events are:
1204 .B DeviceDisappeared
1205 An md array which previously was configured appears to no longer be
1206 configured. (syslog priority: Critical)
1210 was told to monitor an array which is RAID0 or Linear, then it will
1212 .B DeviceDisappeared
1213 with the extra information
1215 This is because RAID0 and Linear do not support the device-failed,
1216 hot-spare and resync operations which are monitored.
1220 An md array started reconstruction. (syslog priority: Warning)
1226 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1227 percentage of the total. (syslog priority: Warning)
1231 An md array that was rebuilding, isn't any more, either because it
1232 finished normally or was aborted. (syslog priority: Warning)
1236 An active component device of an array has been marked as
1237 faulty. (syslog priority: Critical)
1241 A spare component device which was being rebuilt to replace a faulty
1242 device has failed. (syslog priority: Critial)
1246 A spare component device which was being rebuilt to replace a faulty
1247 device as been successfully rebuild and has been made active.
1248 (syslog priority: Info)
1252 A new md array has been detected in the
1254 file. (syslog priority: Info)
1258 A newly noticed array appears to be degraded. This message is not
1261 notices a drive failure which causes degradation, but only when
1263 notices that an array is degraded when it first sees the array.
1264 (syslog priority: Critial)
1268 A spare drive has been moved from one array in a
1270 to another to allow a failed drive to be replaced.
1271 (syslog priority: Info)
1277 has been told, via the config file, that an array should have a certain
1278 number of spare devices, and
1280 detects that it has fewer that this number when it first sees the
1281 array, it will report a
1284 (syslog priority: Info)
1288 An array was found at startup, and the
1291 (syslog priority: Info)
1300 cause Email to be sent. All events cause the program to be run.
1301 The program is run with two or three arguments, they being the event
1302 name, the array device and possibly a second device.
1304 Each event has an associated array device (e.g.
1306 and possibly a second device. For
1311 the second device is the relevant component device.
1314 the second device is the array that the spare was moved from.
1318 to move spares from one array to another, the different arrays need to
1319 be labelled with the same
1321 in the configuration file. The
1323 name can be any string. It is only necessary that different spare
1324 groups use different names.
1328 detects that an array which is in a spare group has fewer active
1329 devices than necessary for the complete array, and has no spare
1330 devices, it will look for another array in the same spare group that
1331 has a full complement of working drive and a spare. It will then
1332 attempt to remove the spare from the second drive and add it to the
1334 If the removal succeeds but the adding fails, then it is added back to
1338 The GROW mode is used for changing the size or shape of an active
1340 For this to work, the kernel must support the necessary change.
1341 Various types of growth may be added during 2.6 development, possibly
1342 including restructuring a raid5 array to have more active devices.
1344 Currently the only support available is to
1346 change the "size" attribute
1347 for RAID1, RAID5 and RAID6.
1349 change the "raid-disks" attribute of RAID1.
1351 add a write-intent bitmap to a RAID1 array.
1354 Normally when an array is built the "size" it taken from the smallest
1355 of the drives. If all the small drives in an arrays are, one at a
1356 time, removed and replaced with larger drives, then you could have an
1357 array of large drives with only a small amount used. In this
1358 situation, changing the "size" with "GROW" mode will allow the extra
1359 space to start being used. If the size is increased in this way, a
1360 "resync" process will start to make sure the new parts of the array
1363 Note that when an array changes size, any filesystem that may be
1364 stored in the array will not automatically grow to use the space. The
1365 filesystem will need to be explicitly told to use the extra space.
1367 A RAID1 array can work with any number of devices from 1 upwards
1368 (though 1 is not very useful). There may be times which you want to
1369 increase or decrease the number of active devices. Note that this is
1370 different to hot-add or hot-remove which changes the number of
1373 When reducing the number of devices in a RAID1 array, the slots which
1374 are to be removed from the array must already be vacant. That is, the
1375 devices that which were in those slots must be failed and removed.
1377 When the number of devices is increased, any hot spares that are
1378 present will be activated immediately.
1380 A write-intent bitmap can be added to, or remove from, an active RAID1
1381 array. Either internal bitmap, of bitmaps stored in a separate file
1382 can be added. Note that if you add a bitmap stored in a file which is
1383 in a filesystem that is on the raid array being affected, the system
1384 will deadlock. The bitmap must be on a separate filesystem.
1388 .B " mdadm --query /dev/name-of-device"
1390 This will find out if a given device is a raid array, or is part of
1391 one, and will provide brief information about the device.
1393 .B " mdadm --assemble --scan"
1395 This will assemble and start all arrays listed in the standard confile
1396 file. This command will typically go in a system startup file.
1398 .B " mdadm --stop --scan"
1400 This will shut down all array that can be shut down (i.e. are not
1401 currently in use). This will typically go in a system shutdown script.
1403 .B " mdadm --follow --scan --delay=120"
1405 If (and only if) there is an Email address or program given in the
1406 standard config file, then
1407 monitor the status of all arrays listed in that file by
1408 polling them ever 2 minutes.
1410 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1412 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1415 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1417 .B " mdadm --detail --scan >> mdadm.conf"
1419 This will create a prototype config file that describes currently
1420 active arrays that are known to be made from partitions of IDE or SCSI drives.
1421 This file should be reviewed before being used as it may
1422 contain unwanted detail.
1424 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1426 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1428 This will find what arrays could be assembled from existign IDE and
1429 SCSI whole drives (not partitions) and store the information is the
1430 format of a config file.
1431 This file is very likely to contain unwanted detail, particularly
1434 entries. It should be reviewed and edited before being used as an
1437 .B " mdadm --examine --brief --scan --config=partitions"
1439 .B " mdadm -Ebsc partitions"
1441 Create a list of devices by reading
1442 .BR /proc/partitions ,
1443 scan these for RAID superblocks, and printout a brief listing of all
1446 .B " mdadm -Ac partitions -m 0 /dev/md0"
1448 Scan all partitions and devices listed in
1449 .BR /proc/partitions
1452 out of all such devices with a RAID superblock with a minor number of 0.
1454 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1456 If config file contains a mail address or alert program, run mdadm in
1457 the background in monitor mode monitoring all md devices. Also write
1458 pid of mdadm daemon to
1459 .BR /var/run/mdadm .
1461 .B " mdadm --create --help"
1463 Providew help about the Create mode.
1465 .B " mdadm --config --help"
1467 Provide help about the format of the config file.
1471 Provide general help.
1482 lists all active md devices with information about them.
1484 uses this to find arrays when
1486 is given in Misc mode, and to monitor array reconstruction
1492 The config file lists which devices may be scanned to see if
1493 they contain MD super block, and gives identifying information
1494 (e.g. UUID) about known MD arrays. See
1500 While entries in the /dev directory can have any format you like,
1502 has an understanding of 'standard' formats which it uses to guide its
1503 behaviour when creating device files via the
1507 The standard names for non-partitioned arrays (the only sort of md
1508 array available in 2.4 and earlier) either of
1514 where NN is a number.
1515 The standard names for partitionable arrays (as available from 2.6
1522 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1526 was previously known as
1530 is completely separate from the
1532 package, and does not use the
1534 configuration file at all.
1537 For information on the various levels of
1541 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1542 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1545 '''for new releases of the RAID driver check out:
1548 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1549 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1554 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1555 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1558 The lastest version of
1560 should always be available from
1562 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1563 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob