4 mdadm \- manage MD devices
10 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
13 RAID devices are virtual devices created from two or more
14 real block devices. This allows multiple devices (typically disk
15 drives or partitions there-of) to be combined into a single device to
16 hold (for example) a single filesystem.
17 Some RAID levels include redundancy and so can survive some degree of
20 Linux Software RAID devices are implemented through the md (Multiple
21 Devices) device driver.
23 Currently, Linux supports
39 is not a Software RAID mechanism, but does involve
42 each device is a path to one common physical storage device.
45 is also not true RAID, and it only involves one device. It
46 provides a layer over a true device that can be used to inject faults.
49 '''is a program that can be used to create, manage, and monitor
51 '''such it provides a similar set of functionality to the
54 '''The key differences between
61 '''is a single program and not a collection of programs.
64 '''can perform (almost) all of its functions without having a
65 '''configuration file and does not use one by default. Also
67 '''helps with management of the configuration
71 '''can provide information about your arrays (through Query, Detail, and Examine)
81 '''configuration file, at all. It has a different configuration file
82 '''with a different format and a different purpose.
85 mdadm has 7 major modes of operation:
88 Assemble the parts of a previously created
89 array into an active array. Components can be explicitly given
90 or can be searched for.
92 checks that the components
93 do form a bona fide array, and can, on request, fiddle superblock
94 information so as to assemble a faulty array.
98 Build an array that doesn't have per-device superblocks. For these
101 cannot differentiate between initial creation and subsequent assembly
102 of an array. It also cannot perform any checks that appropriate
103 devices have been requested. Because of this, the
105 mode should only be used together with a complete understanding of
110 Create a new array with per-device superblocks.
112 '''in several step create-add-add-run or it can all happen with one command.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for raid1, 4, 5, 6, 10 or multipath arrays as
118 only these have interesting state. raid0 or linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices in RAID level 1/4/5/6 and changing the number of
126 active devices in RAID1.
130 This is for doing things to specific components of an array such as
131 adding new spares and removing faulty devices.
135 This is an 'everything else' mode that supports operations on active
136 arrays, operations on component devices such as erasing old superblocks, and
137 information gathering operations.
138 '''This mode allows operations on independent devices such as examine MD
139 '''superblocks, erasing old superblocks and stopping active arrays.
143 .SH Options for selecting a mode are:
146 .BR -A ", " --assemble
147 Assemble a pre-existing array.
151 Build a legacy array without superblocks.
158 .BR -F ", " --follow ", " --monitor
165 Change the size or shape of an active array.
167 If a device is given before any options, or if the first option is
172 then the MANAGE mode is assume.
173 Anything other than these will cause the
177 .SH Options that are not mode-specific are:
181 Display general help message or, after one of the above options, a
182 mode specific help message.
186 Display more detailed help about command line parsing and some commonly
190 .BR -V ", " --version
191 Print version information for mdadm.
194 .BR -v ", " --verbose
195 Be more verbose about what is happening. This can be used twice to be
197 The extra verbosity currently only affects
200 .BR "--examine --scan" .
204 Avoid printing purely informative messages. With this,
206 will be silent unless there is something really important to report.
210 Be less verbose. This is used with
218 gives an intermediate level of verbosity.
222 Be more forceful about certain operations. See the various modes of
223 the exact meaning of this option in different contexts.
226 .BR -c ", " --config=
227 Specify the config file. Default is to use
228 .BR /etc/mdadm.conf ,
229 or if that is missing, then
230 .BR /etc/mdadm/mdadm.conf .
231 If the config file given is
233 then nothing will be read, but
235 will act as though the config file contained exactly
236 .B "DEVICE partitions"
239 to find a list of devices to scan.
242 is given for the config file, then
244 will act as though the config file were empty.
250 for missing information.
251 In general, this option gives
253 permission to get any missing information, like component devices,
254 array devices, array identities, and alert destination from the
256 .BR /etc/mdadm.conf .
257 One exception is MISC mode when using
263 says to get a list of array devices from
267 .B -e ", " --metadata=
268 Declare the style of superblock (raid metadata) to be used. The
269 default is 0.90 for --create, and to guess for other operations.
273 .IP "0, 0.90, default"
274 Use the original 0.90 format superblock. This format limits arrays to
275 28 componenet devices and limits component devices of levels 1 and
276 greater to 2 terabytes.
277 .IP "1, 1.0, 1.1, 1.2"
278 Use the new version-1 format superblock. This has few restrictions.
279 The different subversion store the superblock at different locations
280 on the device, either at the end (for 1.0), at the start (for 1.1) or
281 4K from the start (for 1.2).
284 .SH For create, build, or grow:
287 .BR -n ", " --raid-devices=
288 Specify the number of active devices in the array. This, plus the
289 number of spare devices (see below) must equal the number of
291 (including "\fBmissing\fP" devices)
292 that are listed on the command line for
294 Setting a value of 1 is probably
295 a mistake and so requires that
297 be specified first. A value of 1 will then be allowed for linear,
298 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
300 This number can only be changed using
302 for RAID1 arrays, and only on kernels which provide necessary support.
305 .BR -x ", " --spare-devices=
306 Specify the number of spare (eXtra) devices in the initial array.
307 Spares can also be added
308 and removed later. The number of component devices listed
309 on the command line must equal the number of raid devices plus the
310 number of spare devices.
315 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
316 This must be a multiple of the chunk size, and must leave about 128Kb
317 of space at the end of the drive for the RAID superblock.
318 If this is not specified
319 (as it normally is not) the smallest drive (or partition) sets the
320 size, though if there is a variance among the drives of greater than 1%, a warning is
323 This value can be set with
325 for RAID level 1/4/5/6. If the array was created with a size smaller
326 than the currently active drives, the extra space can be accessed
329 The size can be given as
331 which means to choose the largest size that fits on all current drives.
335 Specify chunk size of kibibytes. The default is 64.
339 Specify rounding factor for linear array (==chunk size)
343 Set raid level. When used with
345 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
346 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty. Obviously some of these are synonymous.
350 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
352 Not yet supported with
356 .BR -p ", " --layout=
357 This option configures the fine details of data layout for raid5,
358 and raid10 arrays, and controls the failure modes for
361 The layout of the raid5 parity block can be one of
366 la, ra, ls, rs. The default is left-symmetric.
368 When setting the failure mode for
386 Each mode can be followed by a number which is used as a period
387 between fault generation. Without a number, the fault is generated
388 once on the first relevant request. With a number, the fault will be
389 generated after that many request, and will continue to be generated
390 every time the period elapses.
392 Multiple failure modes can be current simultaneously by using the
393 "--grow" option to set subsequent failure modes.
395 "clear" or "none" will remove any pending or periodic failure modes,
396 and "flush" will clear any persistent faults.
398 To set the parity with "--grow", the level of the array ("faulty")
399 must be specified before the fault mode is specified.
401 Finally, the layout options for RAID10 are one of 'n', 'o' or 'p' followed
402 by a small number. The default is 'n2'.
405 signals 'near' copies. Multiple copies of one data block are at
406 similar offsets in different devices.
409 signals 'offset' copies. Rather than the chunks being duplicated
410 within a stripe, whole stripes are duplicated but are rotated by one
411 device so duplicate blocks are on different devices. Thus subsequent
412 copies of a block are in the next drive, and are one chunk further
417 (multiple copies have very different offsets). See md(4) for more
418 detail about 'near' and 'far'.
420 The number is the number of copies of each datablock. 2 is normal, 3
421 can be useful. This number can be at most equal to the number of
422 devices in the array. It does not need to divide evenly into that
423 number (e.g. it is perfectly legal to have an 'n2' layout for an array
424 with an odd number of devices).
428 same as --layout (thus explaining the p of
432 .BR -b ", " --bitmap=
433 Specify a file to store a write-intent bitmap in. The file should not
434 exist unless --force is also given. The same file should be provided
435 when assembling the array. If the word
437 is given, then the bitmap is stored with the metadata on the array,
438 and so is replicated on all devices. If the word
442 mode, then any bitmap that is present is removed.
444 To help catch typing errors, the filename must contain at least one
445 slash ('/') if it is a real file (not 'internal' or 'none').
447 Note: external bitmaps are only known to work on ext2 and ext3.
448 Storing bitmap files on other filesystems may result in serious problems.
452 Set the chunksize of the bitmap. Each bit corresponds to that many
453 Kilobytes of storage.
454 When using a file based bitmap, the default is to use the smallest
455 size that is atleast 4 and requires no more than 2^21 chunks.
458 bitmap, the chunksize is automatically determined to make best use of
463 .BR -W ", " --write-mostly
464 subsequent devices lists in a
469 command will be flagged as 'write-mostly'. This is valid for RAID1
470 only and means that the 'md' driver will avoid reading from these
471 devices if at all possible. This can be useful if mirroring over a
476 Specify that write-behind mode should be enabled (valid for RAID1
477 only). If an argument is specified, it will set the maximum number
478 of outstanding writes allowed. The default value is 256.
479 A write-intent bitmap is required in order to use write-behind
480 mode, and write-behind is only attempted on drives marked as
487 that the array pre-existed and is known to be clean. It can be useful
488 when trying to recover from a major failure as you can be sure that no
489 data will be affected unless you actually write to the array. It can
490 also be used when creating a RAID1 or RAID10 if you want to avoid the
491 initial resync, however this practice - while normally safe - is not
492 recommended. Use this ony if you really know what you are doing.
496 This is needed when --grow is used to increase the number of
497 raid-devices in a RAID5 if there are no spare devices available.
498 See the section below on RAID_DEVICE CHANGES. The file should be
499 stored on a separate device, not on the raid array being reshaped.
505 for the array. This is currently only effective when creating an
506 array with a version-1 superblock. The name is a simple textual
507 string that can be used to identify array components when assembling.
513 run the array, even if some of the components
514 appear to be active in another array or filesystem. Normally
516 will ask for confirmation before including such components in an
517 array. This option causes that question to be suppressed.
523 accept the geometry and layout specified without question. Normally
525 will not allow creation of an array with only one device, and will try
526 to create a raid5 array with one missing drive (as this makes the
527 initial resync work faster). With
530 will not try to be so clever.
533 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
534 Instruct mdadm to create the device file if needed, possibly allocating
535 an unused minor number. "md" causes a non-partitionable array
536 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
537 later) to be used. "yes" requires the named md device to have
538 a 'standard' format, and the type and minor number will be determined
539 from this. See DEVICE NAMES below.
541 The argument can also come immediately after
546 is also given, then any
548 entries in the config file will over-ride the
550 instruction given on the command line.
552 For partitionable arrays,
554 will create the device file for the whole array and for the first 4
555 partitions. A different number of partitions can be specified at the
556 end of this option (e.g.
558 If the device name ends with a digit, the partition names add a 'p',
559 and a number, e.g. "/dev/home1p3". If there is no
560 trailing digit, then the partition names just have a number added,
561 e.g. "/dev/scratch3".
563 If the md device name is in a 'standard' format as described in DEVICE
564 NAMES, then it will be created, if necessary, with the appropriate
565 number based on that name. If the device name is not in one of these
566 formats, then a unused minor number will be allocated. The minor
567 number will be considered unused if there is no active array for that
568 number, and there is no entry in /dev for that number and with a
575 uuid of array to assemble. Devices which don't have this uuid are
579 .BR -m ", " --super-minor=
580 Minor number of device that array was created for. Devices which
581 don't have this minor number are excluded. If you create an array as
582 /dev/md1, then all superblocks will contain the minor number 1, even if
583 the array is later assembled as /dev/md2.
585 Giving the literal word "dev" for
589 to use the minor number of the md device that is being assembled.
593 will look for super blocks with a minor number of 0.
597 Specify the name of the array to assemble. This must be the name
598 that was specified when creating the array. It must either match
599 then name stored in the superblock exactly, or it must match
602 is added to the start of the given name.
606 Assemble the array even if some superblocks appear out-of-date
610 Attempt to start the array even if fewer drives were given than were
611 present last time the array was active. Normally if not all the
612 expected drives are found and
614 is not used, then the array will be assembled but not started.
617 an attempt will be made to start it anyway.
621 This is the reverse of
623 in that it inhibits the started if array unless all expected drives
624 are present. This is only needed with
626 and can be used if you physical connections to devices are
627 not as reliable as you would like.
630 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
631 See this option under Create and Build options.
634 .BR -b ", " --bitmap=
635 Specify the bitmap file that was given when the array was created. If
638 bitmap, there is no need to specify this when assembling the array.
644 was used to grow the number of raid-devices in a RAID5, and the system
645 crashed during the critical section, then the same
647 must be presented to --assemble to allow possibly corrupted data to be
651 .BR -U ", " --update=
652 Update the superblock on each device while assembling the array. The
653 argument given to this flag can be one of
666 option will adjust the superblock of an array what was created on a Sparc
667 machine running a patched 2.2 Linux kernel. This kernel got the
668 alignment of part of the superblock wrong. You can use the
669 .B "--examine --sparc2.2"
672 to see what effect this would have.
676 option will update the
678 field on each superblock to match the minor number of the array being
679 assembled. This is not needed on 2.6 and later kernels as they make
680 this adjustment automatically.
684 option will change the uuid of the array. If a UUID is given with the
685 "--uuid" option that UUID will be used as a new UUID and with
687 be used to help identify the devices in the array.
688 If no "--uuid" is given, a random uuid is chosen.
692 option will change the
694 of the array as stored in the superblock. This is only supported for
695 version-1 superblocks.
699 option will change the
701 as recorded in the superblock. For version-0 superblocks, this is the
702 same as updating the UUID.
703 For version-1 superblocks, this involves updating the name.
707 option will cause the array to be marked
709 meaning that any redundancy in the array (e.g. parity for raid5,
710 copies for raid1) may be incorrect. This will cause the raid system
711 to perform a "resync" pass to make sure that all redundant information
716 option allows arrays to be moved between machines with different
718 When assembling such an array for the first time after a move, giving
719 .B "--update=byteorder"
722 to expect superblocks to have their byteorder reversed, and will
723 correct that order before assembling the array. This is only valid
724 with original (Version 0.90) superblocks.
728 option will correct the summaries in the superblock. That is the
729 counts of total, working, active, failed, and spare devices.
735 hot-add listed devices.
739 re-add a device that was recently removed from an array.
743 remove listed devices. They must not be active. i.e. they should
744 be failed or spare devices.
748 mark listed devices as faulty.
755 Each of these options require that the first device list is the array
756 to be acted upon and the remainder are component devices to be added,
757 removed, or marked as fault. Several different operations can be
758 specified for different devices, e.g.
760 mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
762 Each operation applies to all devices listed until the next
765 If an array is using a write-intent bitmap, then devices which have
766 been removed can be re-added in a way that avoids a full
767 reconstruction but instead just updated the blocks that have changed
768 since the device was removed. For arrays with persistent metadata
769 (superblocks) this is done automatically. For arrays created with
771 mdadm needs to be told that this device we removed recently with
774 Devices can only be removed from an array if they are not in active
775 use. i.e. that must be spares or failed devices. To remove an active
776 device, it must be marked as
784 Examine a device to see
785 (1) if it is an md device and (2) if it is a component of an md
787 Information about what is discovered is presented.
791 Print detail of one or more md devices.
794 .BR -E ", " --examine
795 Print content of md superblock on device(s).
798 If an array was created on a 2.2 Linux kernel patched with RAID
799 support, the superblock will have been created incorrectly, or at
800 least incompatibly with 2.4 and later kernels. Using the
804 will fix the superblock before displaying it. If this appears to do
805 the right thing, then the array can be successfully assembled using
806 .BR "--assemble --update=sparc2.2" .
809 .BR -X ", " --examine-bitmap
810 Report information about a bitmap file.
814 start a partially built array.
818 deactivate array, releasing all resources.
821 .BR -o ", " --readonly
822 mark array as readonly.
825 .BR -w ", " --readwrite
826 mark array as readwrite.
830 If the device contains a valid md superblock, the block is
831 over-written with zeros. With
833 the block where the superblock would be is over-written even if it
834 doesn't appear to be valid.
842 is set to reflect the status of the device.
844 .SH For Monitor mode:
847 Give a mail address to send alerts to.
850 .BR -p ", " --program ", " --alert
851 Give a program to be run whenever an event is detected.
855 Cause all events to be reported through 'syslog'. The messages have
856 facility of 'daemon' and varying priorities.
860 Give a delay in seconds.
862 polls the md arrays and then waits this many seconds before polling
863 again. The default is 60 seconds.
866 .BR -f ", " --daemonise
869 to run as a background daemon if it decides to monitor anything. This
870 causes it to fork and run in the child, and to disconnect form the
871 terminal. The process id of the child is written to stdout.
874 which will only continue monitoring if a mail address or alert program
875 is found in the config file.
878 .BR -i ", " --pid-file
881 is running in daemon mode, write the pid of the daemon process to
882 the specified file, instead of printing it on standard output.
885 .BR -1 ", " --oneshot
886 Check arrays only once. This will generate
888 events and more significantly
894 .B " mdadm --monitor --scan -1"
896 from a cron script will ensure regular notification of any degraded arrays.
902 alert for every array found at startup. This alert gets mailed and
903 passed to the alert program. This can be used for testing that alert
904 message do get through successfully.
911 .I md-device options-and-component-devices...
914 .B mdadm --assemble --scan
915 .I md-devices-and-options...
918 .B mdadm --assemble --scan
922 This usage assembles one or more raid arrays from pre-existing components.
923 For each array, mdadm needs to know the md device, the identity of the
924 array, and a number of component-devices. These can be found in a number of ways.
926 In the first usage example (without the
928 the first device given is the md device.
929 In the second usage example, all devices listed are treated as md
930 devices and assembly is attempted.
931 In the third (where no devices are listed) all md devices that are
932 listed in the configuration file are assembled.
934 If precisely one device is listed, but
940 was given and identify information is extracted from the configuration file.
942 The identity can be given with the
946 option, can be found in the config file, or will be taken from the
947 super block on the first component-device listed on the command line.
949 Devices can be given on the
951 command line or in the config file. Only devices which have an md
952 superblock which contains the right identity will be considered for
955 The config file is only used if explicitly named with
957 or requested with (a possibly implicit)
965 is not given, then the config file will only be used to find the
966 identity of md arrays.
968 Normally the array will be started after it is assembled. However if
970 is not given and insufficient drives were listed to start a complete
971 (non-degraded) array, then the array is not started (to guard against
972 usage errors). To insist that the array be started in this case (as
973 may work for RAID1, 4, 5, 6, or 10), give the
979 option is given, either on the command line (--auto) or in the
980 configuration file (e.g. auto=part), then
982 will create the md device if necessary or will re-create it if it
983 doesn't look usable as it is.
985 This can be useful for handling partitioned devices (which don't have
986 a stable device number - it can change after a reboot) and when using
987 "udev" to manage your
989 tree (udev cannot handle md devices because of the unusual device
990 initialisation conventions).
992 If the option to "auto" is "mdp" or "part" or (on the command line
993 only) "p", then mdadm will create a partitionable array, using the
994 first free one that is not in use, and does not already have an entry
995 in /dev (apart from numeric /dev/md* entries).
997 If the option to "auto" is "yes" or "md" or (on the command line)
998 nothing, then mdadm will create a traditional, non-partitionable md
1001 It is expected that the "auto" functionality will be used to create
1002 device entries with meaningful names such as "/dev/md/home" or
1003 "/dev/md/root", rather than names based on the numerical array number.
1005 When using this option to create a partitionable array, the device
1006 files for the first 4 partitions are also created. If a different
1007 number is required it can be simply appended to the auto option.
1008 e.g. "auto=part8". Partition names are created by appending a digit
1009 string to the device name, with an intervening "p" if the device name
1014 option is also available in Build and Create modes. As those modes do
1015 not use a config file, the "auto=" config option does not apply to
1026 .BI --raid-devices= Z
1030 This usage is similar to
1032 The difference is that it creates an array without a superblock. With
1033 these arrays there is no difference between initially creating the array and
1034 subsequently assembling the array, except that hopefully there is useful
1035 data there in the second case.
1037 The level may raid0, linear, multipath, or faulty, or one of their
1038 synonyms. All devices must be listed and the array will be started
1050 .BI --raid-devices= Z
1054 This usage will initialise a new md array, associate some devices with
1055 it, and activate the array.
1059 option is given (as described in more detail in the section on
1060 Assemble mode), then the md device will be created with a suitable
1061 device number if necessary.
1063 As devices are added, they are checked to see if they contain raid
1064 superblocks or filesystems. They are also checked to see if the variance in
1065 device size exceeds 1%.
1067 If any discrepancy is found, the array will not automatically be run, though
1070 can override this caution.
1072 To create a "degraded" array in which some devices are missing, simply
1073 give the word "\fBmissing\fP"
1074 in place of a device name. This will cause
1076 to leave the corresponding slot in the array empty.
1077 For a RAID4 or RAID5 array at most one slot can be
1078 "\fBmissing\fP"; for a RAID6 array at most two slots.
1079 For a RAID1 array, only one real device needs to be given. All of the
1083 When creating a RAID5 array,
1085 will automatically create a degraded array with an extra spare drive.
1086 This is because building the spare into a degraded array is in general faster than resyncing
1087 the parity on a non-degraded, but not clean, array. This feature can
1088 be over-ridden with the
1094 '''option is given, it is not necessary to list any component-devices in this command.
1095 '''They can be added later, before a
1099 '''is given, the apparent size of the smallest drive given is used.
1101 The General Management options that are valid with --create are:
1104 insist on running the array even if some devices look like they might
1109 start the array readonly - not supported yet.
1117 .I options... devices...
1120 This usage will allow individual devices in an array to be failed,
1121 removed or added. It is possible to perform multiple operations with
1122 on command. For example:
1124 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1130 and will then remove it from the array and finally add it back
1131 in as a spare. However only one md array can be affected by a single
1142 MISC mode includes a number of distinct operations that
1143 operate on distinct devices. The operations are:
1146 The device is examined to see if it is
1147 (1) an active md array, or
1148 (2) a component of an md array.
1149 The information discovered is reported.
1153 The device should be an active md device.
1155 will display a detailed description of the array.
1159 will cause the output to be less detailed and the format to be
1160 suitable for inclusion in
1161 .BR /etc/mdadm.conf .
1164 will normally be 0 unless
1166 failed to get useful information about the device(s). However if the
1168 option is given, then the exit status will be:
1172 The array is functioning normally.
1175 The array has at least one failed device.
1178 The array has multiple failed devices and hence is unusable (raid4 or
1182 There was an error while trying to get information about the device.
1187 The device should be a component of an md array.
1189 will read the md superblock of the device and display the contents.
1194 then multiple devices that are components of the one array
1195 are grouped together and reported in a single entry suitable
1197 .BR /etc/mdadm.conf .
1201 without listing any devices will cause all devices listed in the
1202 config file to be examined.
1206 The devices should be active md arrays which will be deactivated, as
1207 long as they are not currently in use.
1211 This will fully activate a partially assembled md array.
1215 This will mark an active array as read-only, providing that it is
1216 not currently being used.
1222 array back to being read/write.
1226 For all operations except
1229 will cause the operation to be applied to all arrays listed in
1234 causes all devices listed in the config file to be examined.
1242 .I options... devices...
1247 to periodically poll a number of md arrays and to report on any events
1250 will never exit once it decides that there are arrays to be checked,
1251 so it should normally be run in the background.
1253 As well as reporting events,
1255 may move a spare drive from one array to another if they are in the
1258 and if the destination array has a failed drive but no spares.
1260 If any devices are listed on the command line,
1262 will only monitor those devices. Otherwise all arrays listed in the
1263 configuration file will be monitored. Further, if
1265 is given, then any other md devices that appear in
1267 will also be monitored.
1269 The result of monitoring the arrays is the generation of events.
1270 These events are passed to a separate program (if specified) and may
1271 be mailed to a given E-mail address.
1273 When passing event to program, the program is run once for each event
1274 and is given 2 or 3 command-line arguments. The first is the
1275 name of the event (see below). The second is the name of the
1276 md device which is affected, and the third is the name of a related
1277 device if relevant, such as a component device that has failed.
1281 is given, then a program or an E-mail address must be specified on the
1282 command line or in the config file. If neither are available, then
1284 will not monitor anything.
1288 will continue monitoring as long as something was found to monitor. If
1289 no program or email is given, then each event is reported to
1292 The different events are:
1296 .B DeviceDisappeared
1297 An md array which previously was configured appears to no longer be
1298 configured. (syslog priority: Critical)
1302 was told to monitor an array which is RAID0 or Linear, then it will
1304 .B DeviceDisappeared
1305 with the extra information
1307 This is because RAID0 and Linear do not support the device-failed,
1308 hot-spare and resync operations which are monitored.
1312 An md array started reconstruction. (syslog priority: Warning)
1318 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1319 percentage of the total. (syslog priority: Warning)
1323 An md array that was rebuilding, isn't any more, either because it
1324 finished normally or was aborted. (syslog priority: Warning)
1328 An active component device of an array has been marked as
1329 faulty. (syslog priority: Critical)
1333 A spare component device which was being rebuilt to replace a faulty
1334 device has failed. (syslog priority: Critial)
1338 A spare component device which was being rebuilt to replace a faulty
1339 device has been successfully rebuilt and has been made active.
1340 (syslog priority: Info)
1344 A new md array has been detected in the
1346 file. (syslog priority: Info)
1350 A newly noticed array appears to be degraded. This message is not
1353 notices a drive failure which causes degradation, but only when
1355 notices that an array is degraded when it first sees the array.
1356 (syslog priority: Critial)
1360 A spare drive has been moved from one array in a
1362 to another to allow a failed drive to be replaced.
1363 (syslog priority: Info)
1369 has been told, via the config file, that an array should have a certain
1370 number of spare devices, and
1372 detects that it has fewer that this number when it first sees the
1373 array, it will report a
1376 (syslog priority: Warning)
1380 An array was found at startup, and the
1383 (syslog priority: Info)
1393 cause Email to be sent. All events cause the program to be run.
1394 The program is run with two or three arguments, they being the event
1395 name, the array device and possibly a second device.
1397 Each event has an associated array device (e.g.
1399 and possibly a second device. For
1404 the second device is the relevant component device.
1407 the second device is the array that the spare was moved from.
1411 to move spares from one array to another, the different arrays need to
1412 be labelled with the same
1414 in the configuration file. The
1416 name can be any string. It is only necessary that different spare
1417 groups use different names.
1421 detects that an array which is in a spare group has fewer active
1422 devices than necessary for the complete array, and has no spare
1423 devices, it will look for another array in the same spare group that
1424 has a full complement of working drive and a spare. It will then
1425 attempt to remove the spare from the second drive and add it to the
1427 If the removal succeeds but the adding fails, then it is added back to
1431 The GROW mode is used for changing the size or shape of an active
1433 For this to work, the kernel must support the necessary change.
1434 Various types of growth are being added during 2.6 development,
1435 including restructuring a raid5 array to have more active devices.
1437 Currently the only support available is to
1439 change the "size" attribute
1440 for RAID1, RAID5 and RAID6.
1442 increase the "raid-disks" attribute of RAID1 and RAID5.
1444 add a write-intent bitmap to any array which support these bitmaps, or
1445 remove a write-intent bitmap from such an array.
1449 Normally when an array is built the "size" it taken from the smallest
1450 of the drives. If all the small drives in an arrays are, one at a
1451 time, removed and replaced with larger drives, then you could have an
1452 array of large drives with only a small amount used. In this
1453 situation, changing the "size" with "GROW" mode will allow the extra
1454 space to start being used. If the size is increased in this way, a
1455 "resync" process will start to make sure the new parts of the array
1458 Note that when an array changes size, any filesystem that may be
1459 stored in the array will not automatically grow to use the space. The
1460 filesystem will need to be explicitly told to use the extra space.
1462 .SS RAID-DEVICES CHANGES
1464 A RAID1 array can work with any number of devices from 1 upwards
1465 (though 1 is not very useful). There may be times which you want to
1466 increase or decrease the number of active devices. Note that this is
1467 different to hot-add or hot-remove which changes the number of
1470 When reducing the number of devices in a RAID1 array, the slots which
1471 are to be removed from the array must already be vacant. That is, the
1472 devices that which were in those slots must be failed and removed.
1474 When the number of devices is increased, any hot spares that are
1475 present will be activated immediately.
1477 Increasing the number of active devices in a RAID5 is much more
1478 effort. Every block in the array will need to be read and written
1479 back to a new location. From 2.6.17, the Linux Kernel is able to do
1480 this safely, including restart and interrupted "reshape".
1482 When relocating the first few stripes on a raid5, it is not possible
1483 to keep the data on disk completely consistent and crash-proof. To
1484 provide the required safety, mdadm disables writes to the array while
1485 this "critical section" is reshaped, and takes a backup of the data
1486 that is in that section. This backup is normally stored in any spare
1487 devices that the array has, however it can also be stored in a
1488 separate file specified with the
1490 option. If this option is used, and the system does crash during the
1491 critical period, the same file must be passed to
1493 to restore the backup and reassemble the array.
1497 A write-intent bitmap can be added to, or removed from, an active
1498 array. Either internal bitmaps, or bitmaps stored in a separate file
1499 can be added. Note that if you add a bitmap stored in a file which is
1500 in a filesystem that is on the raid array being affected, the system
1501 will deadlock. The bitmap must be on a separate filesystem.
1505 .B " mdadm --query /dev/name-of-device"
1507 This will find out if a given device is a raid array, or is part of
1508 one, and will provide brief information about the device.
1510 .B " mdadm --assemble --scan"
1512 This will assemble and start all arrays listed in the standard config file
1513 file. This command will typically go in a system startup file.
1515 .B " mdadm --stop --scan"
1517 This will shut down all array that can be shut down (i.e. are not
1518 currently in use). This will typically go in a system shutdown script.
1520 .B " mdadm --follow --scan --delay=120"
1522 If (and only if) there is an Email address or program given in the
1523 standard config file, then
1524 monitor the status of all arrays listed in that file by
1525 polling them ever 2 minutes.
1527 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1529 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1532 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1534 .B " mdadm --detail --scan >> mdadm.conf"
1536 This will create a prototype config file that describes currently
1537 active arrays that are known to be made from partitions of IDE or SCSI drives.
1538 This file should be reviewed before being used as it may
1539 contain unwanted detail.
1541 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1543 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1545 This will find what arrays could be assembled from existing IDE and
1546 SCSI whole drives (not partitions) and store the information is the
1547 format of a config file.
1548 This file is very likely to contain unwanted detail, particularly
1551 entries. It should be reviewed and edited before being used as an
1554 .B " mdadm --examine --brief --scan --config=partitions"
1556 .B " mdadm -Ebsc partitions"
1558 Create a list of devices by reading
1559 .BR /proc/partitions ,
1560 scan these for RAID superblocks, and printout a brief listing of all
1563 .B " mdadm -Ac partitions -m 0 /dev/md0"
1565 Scan all partitions and devices listed in
1566 .BR /proc/partitions
1569 out of all such devices with a RAID superblock with a minor number of 0.
1571 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1573 If config file contains a mail address or alert program, run mdadm in
1574 the background in monitor mode monitoring all md devices. Also write
1575 pid of mdadm daemon to
1576 .BR /var/run/mdadm .
1578 .B " mdadm --create --help"
1580 Provide help about the Create mode.
1582 .B " mdadm --config --help"
1584 Provide help about the format of the config file.
1588 Provide general help.
1599 lists all active md devices with information about them.
1601 uses this to find arrays when
1603 is given in Misc mode, and to monitor array reconstruction
1609 The config file lists which devices may be scanned to see if
1610 they contain MD super block, and gives identifying information
1611 (e.g. UUID) about known MD arrays. See
1617 While entries in the /dev directory can have any format you like,
1619 has an understanding of 'standard' formats which it uses to guide its
1620 behaviour when creating device files via the
1624 The standard names for non-partitioned arrays (the only sort of md
1625 array available in 2.4 and earlier) either of
1631 where NN is a number.
1632 The standard names for partitionable arrays (as available from 2.6
1639 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1643 was previously known as
1647 is completely separate from the
1649 package, and does not use the
1651 configuration file at all.
1654 For information on the various levels of
1658 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1659 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1662 '''for new releases of the RAID driver check out:
1665 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1666 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1671 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1672 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1675 The latest version of
1677 should always be available from
1679 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1680 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob