2 ''' Copyright Neil Brown and others.
3 ''' This program is free software; you can redistribute it and/or modify
4 ''' it under the terms of the GNU General Public License as published by
5 ''' the Free Software Foundation; either version 2 of the License, or
6 ''' (at your option) any later version.
7 ''' See file COPYING in distribution for details.
10 mdadm \- manage MD devices
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
19 RAID devices are virtual devices created from two or more
20 real block devices. This allows multiple devices (typically disk
21 drives or partitions there-of) to be combined into a single device to
22 hold (for example) a single filesystem.
23 Some RAID levels include redundancy and so can survive some degree of
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
29 Currently, Linux supports
45 is not a Software RAID mechanism, but does involve
48 each device is a path to one common physical storage device.
51 is also not true RAID, and it only involves one device. It
52 provides a layer over a true device that can be used to inject faults.
55 '''is a program that can be used to create, manage, and monitor
57 '''such it provides a similar set of functionality to the
60 '''The key differences between
67 '''is a single program and not a collection of programs.
70 '''can perform (almost) all of its functions without having a
71 '''configuration file and does not use one by default. Also
73 '''helps with management of the configuration
77 '''can provide information about your arrays (through Query, Detail, and Examine)
87 '''configuration file, at all. It has a different configuration file
88 '''with a different format and a different purpose.
91 mdadm has 7 major modes of operation:
94 Assemble the parts of a previously created
95 array into an active array. Components can be explicitly given
96 or can be searched for.
98 checks that the components
99 do form a bona fide array, and can, on request, fiddle superblock
100 information so as to assemble a faulty array.
104 Build an array that doesn't have per-device superblocks. For these
107 cannot differentiate between initial creation and subsequent assembly
108 of an array. It also cannot perform any checks that appropriate
109 devices have been requested. Because of this, the
111 mode should only be used together with a complete understanding of
116 Create a new array with per-device superblocks.
118 '''in several step create-add-add-run or it can all happen with one command.
121 .B "Follow or Monitor"
122 Monitor one or more md devices and act on any state changes. This is
123 only meaningful for raid1, 4, 5, 6, 10 or multipath arrays as
124 only these have interesting state. raid0 or linear never have
125 missing, spare, or failed drives, so there is nothing to monitor.
129 Grow (or shrink) an array, or otherwise reshape it in some way.
130 Currently supported growth options including changing the active size
131 of component devices in RAID level 1/4/5/6 and changing the number of
132 active devices in RAID1.
136 This is for doing things to specific components of an array such as
137 adding new spares and removing faulty devices.
141 This is an 'everything else' mode that supports operations on active
142 arrays, operations on component devices such as erasing old superblocks, and
143 information gathering operations.
144 '''This mode allows operations on independent devices such as examine MD
145 '''superblocks, erasing old superblocks and stopping active arrays.
149 .SH Options for selecting a mode are:
152 .BR -A ", " --assemble
153 Assemble a pre-existing array.
157 Build a legacy array without superblocks.
164 .BR -F ", " --follow ", " --monitor
171 Change the size or shape of an active array.
173 If a device is given before any options, or if the first option is
178 then the MANAGE mode is assume.
179 Anything other than these will cause the
183 .SH Options that are not mode-specific are:
187 Display general help message or, after one of the above options, a
188 mode specific help message.
192 Display more detailed help about command line parsing and some commonly
196 .BR -V ", " --version
197 Print version information for mdadm.
200 .BR -v ", " --verbose
201 Be more verbose about what is happening. This can be used twice to be
203 The extra verbosity currently only affects
206 .BR "--examine --scan" .
210 Avoid printing purely informative messages. With this,
212 will be silent unless there is something really important to report.
216 Be less verbose. This is used with
224 gives an intermediate level of verbosity.
228 Be more forceful about certain operations. See the various modes of
229 the exact meaning of this option in different contexts.
232 .BR -c ", " --config=
233 Specify the config file. Default is to use
234 .BR /etc/mdadm.conf ,
235 or if that is missing, then
236 .BR /etc/mdadm/mdadm.conf .
237 If the config file given is
239 then nothing will be read, but
241 will act as though the config file contained exactly
242 .B "DEVICE partitions"
245 to find a list of devices to scan.
248 is given for the config file, then
250 will act as though the config file were empty.
256 for missing information.
257 In general, this option gives
259 permission to get any missing information, like component devices,
260 array devices, array identities, and alert destination from the
262 .BR /etc/mdadm.conf .
263 One exception is MISC mode when using
269 says to get a list of array devices from
273 .B -e ", " --metadata=
274 Declare the style of superblock (raid metadata) to be used. The
275 default is 0.90 for --create, and to guess for other operations.
279 .IP "0, 0.90, default"
280 Use the original 0.90 format superblock. This format limits arrays to
281 28 componenet devices and limits component devices of levels 1 and
282 greater to 2 terabytes.
283 .IP "1, 1.0, 1.1, 1.2"
284 Use the new version-1 format superblock. This has few restrictions.
285 The different subversion store the superblock at different locations
286 on the device, either at the end (for 1.0), at the start (for 1.1) or
287 4K from the start (for 1.2).
292 This will over-ride any
294 setting in the config file and provides the identify of the host which
295 should be considered the home for any arrays.
297 When creating an array, the
299 will be recorded in the superblock. For version-1 superblocks, it will
300 be prefixed to the array name. For version-0.90 superblocks part of
301 the SHA1 hash of the hostname will be stored in the later half of the
304 When reporting information about an array, any array which is tagged
305 for the given homehost will be reported as such.
307 When using Auto-Assemble, only arrays tagged for the given homehost
310 .SH For create, build, or grow:
313 .BR -n ", " --raid-devices=
314 Specify the number of active devices in the array. This, plus the
315 number of spare devices (see below) must equal the number of
317 (including "\fBmissing\fP" devices)
318 that are listed on the command line for
320 Setting a value of 1 is probably
321 a mistake and so requires that
323 be specified first. A value of 1 will then be allowed for linear,
324 multipath, raid0 and raid1. It is never allowed for raid4 or raid5.
326 This number can only be changed using
328 for RAID1 arrays, and only on kernels which provide necessary support.
331 .BR -x ", " --spare-devices=
332 Specify the number of spare (eXtra) devices in the initial array.
333 Spares can also be added
334 and removed later. The number of component devices listed
335 on the command line must equal the number of raid devices plus the
336 number of spare devices.
341 Amount (in Kibibytes) of space to use from each drive in RAID1/4/5/6.
342 This must be a multiple of the chunk size, and must leave about 128Kb
343 of space at the end of the drive for the RAID superblock.
344 If this is not specified
345 (as it normally is not) the smallest drive (or partition) sets the
346 size, though if there is a variance among the drives of greater than 1%, a warning is
349 This value can be set with
351 for RAID level 1/4/5/6. If the array was created with a size smaller
352 than the currently active drives, the extra space can be accessed
355 The size can be given as
357 which means to choose the largest size that fits on all current drives.
361 Specify chunk size of kibibytes. The default is 64.
365 Specify rounding factor for linear array (==chunk size)
369 Set raid level. When used with
371 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
372 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty. Obviously some of these are synonymous.
376 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
378 Not yet supported with
382 .BR -p ", " --layout=
383 This option configures the fine details of data layout for raid5,
384 and raid10 arrays, and controls the failure modes for
387 The layout of the raid5 parity block can be one of
392 la, ra, ls, rs. The default is left-symmetric.
394 When setting the failure mode for
412 Each mode can be followed by a number which is used as a period
413 between fault generation. Without a number, the fault is generated
414 once on the first relevant request. With a number, the fault will be
415 generated after that many request, and will continue to be generated
416 every time the period elapses.
418 Multiple failure modes can be current simultaneously by using the
419 "--grow" option to set subsequent failure modes.
421 "clear" or "none" will remove any pending or periodic failure modes,
422 and "flush" will clear any persistent faults.
424 To set the parity with "--grow", the level of the array ("faulty")
425 must be specified before the fault mode is specified.
427 Finally, the layout options for RAID10 are one of 'n', 'o' or 'p' followed
428 by a small number. The default is 'n2'.
431 signals 'near' copies. Multiple copies of one data block are at
432 similar offsets in different devices.
435 signals 'offset' copies. Rather than the chunks being duplicated
436 within a stripe, whole stripes are duplicated but are rotated by one
437 device so duplicate blocks are on different devices. Thus subsequent
438 copies of a block are in the next drive, and are one chunk further
443 (multiple copies have very different offsets). See md(4) for more
444 detail about 'near' and 'far'.
446 The number is the number of copies of each datablock. 2 is normal, 3
447 can be useful. This number can be at most equal to the number of
448 devices in the array. It does not need to divide evenly into that
449 number (e.g. it is perfectly legal to have an 'n2' layout for an array
450 with an odd number of devices).
454 same as --layout (thus explaining the p of
458 .BR -b ", " --bitmap=
459 Specify a file to store a write-intent bitmap in. The file should not
460 exist unless --force is also given. The same file should be provided
461 when assembling the array. If the word
463 is given, then the bitmap is stored with the metadata on the array,
464 and so is replicated on all devices. If the word
468 mode, then any bitmap that is present is removed.
470 To help catch typing errors, the filename must contain at least one
471 slash ('/') if it is a real file (not 'internal' or 'none').
473 Note: external bitmaps are only known to work on ext2 and ext3.
474 Storing bitmap files on other filesystems may result in serious problems.
478 Set the chunksize of the bitmap. Each bit corresponds to that many
479 Kilobytes of storage.
480 When using a file based bitmap, the default is to use the smallest
481 size that is atleast 4 and requires no more than 2^21 chunks.
484 bitmap, the chunksize is automatically determined to make best use of
489 .BR -W ", " --write-mostly
490 subsequent devices lists in a
495 command will be flagged as 'write-mostly'. This is valid for RAID1
496 only and means that the 'md' driver will avoid reading from these
497 devices if at all possible. This can be useful if mirroring over a
502 Specify that write-behind mode should be enabled (valid for RAID1
503 only). If an argument is specified, it will set the maximum number
504 of outstanding writes allowed. The default value is 256.
505 A write-intent bitmap is required in order to use write-behind
506 mode, and write-behind is only attempted on drives marked as
513 that the array pre-existed and is known to be clean. It can be useful
514 when trying to recover from a major failure as you can be sure that no
515 data will be affected unless you actually write to the array. It can
516 also be used when creating a RAID1 or RAID10 if you want to avoid the
517 initial resync, however this practice - while normally safe - is not
518 recommended. Use this ony if you really know what you are doing.
522 This is needed when --grow is used to increase the number of
523 raid-devices in a RAID5 if there are no spare devices available.
524 See the section below on RAID_DEVICE CHANGES. The file should be
525 stored on a separate device, not on the raid array being reshaped.
531 for the array. This is currently only effective when creating an
532 array with a version-1 superblock. The name is a simple textual
533 string that can be used to identify array components when assembling.
539 run the array, even if some of the components
540 appear to be active in another array or filesystem. Normally
542 will ask for confirmation before including such components in an
543 array. This option causes that question to be suppressed.
549 accept the geometry and layout specified without question. Normally
551 will not allow creation of an array with only one device, and will try
552 to create a raid5 array with one missing drive (as this makes the
553 initial resync work faster). With
556 will not try to be so clever.
559 .BR -a ", " "--auto{=no,yes,md,mdp,part,p}{NN}"
560 Instruct mdadm to create the device file if needed, possibly allocating
561 an unused minor number. "md" causes a non-partitionable array
562 to be used. "mdp", "part" or "p" causes a partitionable array (2.6 and
563 later) to be used. "yes" requires the named md device to have
564 a 'standard' format, and the type and minor number will be determined
565 from this. See DEVICE NAMES below.
567 The argument can also come immediately after
572 is also given, then any
574 entries in the config file will over-ride the
576 instruction given on the command line.
578 For partitionable arrays,
580 will create the device file for the whole array and for the first 4
581 partitions. A different number of partitions can be specified at the
582 end of this option (e.g.
584 If the device name ends with a digit, the partition names add a 'p',
585 and a number, e.g. "/dev/home1p3". If there is no
586 trailing digit, then the partition names just have a number added,
587 e.g. "/dev/scratch3".
589 If the md device name is in a 'standard' format as described in DEVICE
590 NAMES, then it will be created, if necessary, with the appropriate
591 number based on that name. If the device name is not in one of these
592 formats, then a unused minor number will be allocated. The minor
593 number will be considered unused if there is no active array for that
594 number, and there is no entry in /dev for that number and with a
601 uuid of array to assemble. Devices which don't have this uuid are
605 .BR -m ", " --super-minor=
606 Minor number of device that array was created for. Devices which
607 don't have this minor number are excluded. If you create an array as
608 /dev/md1, then all superblocks will contain the minor number 1, even if
609 the array is later assembled as /dev/md2.
611 Giving the literal word "dev" for
615 to use the minor number of the md device that is being assembled.
619 will look for super blocks with a minor number of 0.
623 Specify the name of the array to assemble. This must be the name
624 that was specified when creating the array. It must either match
625 then name stored in the superblock exactly, or it must match
628 is added to the start of the given name.
632 Assemble the array even if some superblocks appear out-of-date
636 Attempt to start the array even if fewer drives were given than were
637 present last time the array was active. Normally if not all the
638 expected drives are found and
640 is not used, then the array will be assembled but not started.
643 an attempt will be made to start it anyway.
647 This is the reverse of
649 in that it inhibits the started if array unless all expected drives
650 are present. This is only needed with
652 and can be used if you physical connections to devices are
653 not as reliable as you would like.
656 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
657 See this option under Create and Build options.
660 .BR -b ", " --bitmap=
661 Specify the bitmap file that was given when the array was created. If
664 bitmap, there is no need to specify this when assembling the array.
670 was used to grow the number of raid-devices in a RAID5, and the system
671 crashed during the critical section, then the same
673 must be presented to --assemble to allow possibly corrupted data to be
677 .BR -U ", " --update=
678 Update the superblock on each device while assembling the array. The
679 argument given to this flag can be one of
692 option will adjust the superblock of an array what was created on a Sparc
693 machine running a patched 2.2 Linux kernel. This kernel got the
694 alignment of part of the superblock wrong. You can use the
695 .B "--examine --sparc2.2"
698 to see what effect this would have.
702 option will update the
704 field on each superblock to match the minor number of the array being
705 assembled. This is not needed on 2.6 and later kernels as they make
706 this adjustment automatically.
710 option will change the uuid of the array. If a UUID is given with the
711 "--uuid" option that UUID will be used as a new UUID and will
713 be used to help identify the devices in the array.
714 If no "--uuid" is given, a random uuid is chosen.
718 option will change the
720 of the array as stored in the superblock. This is only supported for
721 version-1 superblocks.
725 option will change the
727 as recorded in the superblock. For version-0 superblocks, this is the
728 same as updating the UUID.
729 For version-1 superblocks, this involves updating the name.
733 option will cause the array to be marked
735 meaning that any redundancy in the array (e.g. parity for raid5,
736 copies for raid1) may be incorrect. This will cause the raid system
737 to perform a "resync" pass to make sure that all redundant information
742 option allows arrays to be moved between machines with different
744 When assembling such an array for the first time after a move, giving
745 .B "--update=byteorder"
748 to expect superblocks to have their byteorder reversed, and will
749 correct that order before assembling the array. This is only valid
750 with original (Version 0.90) superblocks.
754 option will correct the summaries in the superblock. That is the
755 counts of total, working, active, failed, and spare devices.
758 .B --auto-update-homehost
759 This flag is only meaning with auto-assembly (see discussion below).
760 In that situation, if no suitable arrays are found for this homehost,
762 will recan for any arrays at all and will assemble them and update the
763 homehost to match the current host.
769 hot-add listed devices.
773 re-add a device that was recently removed from an array.
777 remove listed devices. They must not be active. i.e. they should
778 be failed or spare devices.
782 mark listed devices as faulty.
789 Each of these options require that the first device list is the array
790 to be acted upon and the remainder are component devices to be added,
791 removed, or marked as fault. Several different operations can be
792 specified for different devices, e.g.
794 mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
796 Each operation applies to all devices listed until the next
799 If an array is using a write-intent bitmap, then devices which have
800 been removed can be re-added in a way that avoids a full
801 reconstruction but instead just updated the blocks that have changed
802 since the device was removed. For arrays with persistent metadata
803 (superblocks) this is done automatically. For arrays created with
805 mdadm needs to be told that this device we removed recently with
808 Devices can only be removed from an array if they are not in active
809 use. i.e. that must be spares or failed devices. To remove an active
810 device, it must be marked as
818 Examine a device to see
819 (1) if it is an md device and (2) if it is a component of an md
821 Information about what is discovered is presented.
825 Print detail of one or more md devices.
828 .BR -E ", " --examine
829 Print content of md superblock on device(s).
832 If an array was created on a 2.2 Linux kernel patched with RAID
833 support, the superblock will have been created incorrectly, or at
834 least incompatibly with 2.4 and later kernels. Using the
838 will fix the superblock before displaying it. If this appears to do
839 the right thing, then the array can be successfully assembled using
840 .BR "--assemble --update=sparc2.2" .
843 .BR -X ", " --examine-bitmap
844 Report information about a bitmap file.
848 start a partially built array.
852 deactivate array, releasing all resources.
855 .BR -o ", " --readonly
856 mark array as readonly.
859 .BR -w ", " --readwrite
860 mark array as readwrite.
864 If the device contains a valid md superblock, the block is
865 over-written with zeros. With
867 the block where the superblock would be is over-written even if it
868 doesn't appear to be valid.
876 is set to reflect the status of the device.
878 .SH For Monitor mode:
881 Give a mail address to send alerts to.
884 .BR -p ", " --program ", " --alert
885 Give a program to be run whenever an event is detected.
889 Cause all events to be reported through 'syslog'. The messages have
890 facility of 'daemon' and varying priorities.
894 Give a delay in seconds.
896 polls the md arrays and then waits this many seconds before polling
897 again. The default is 60 seconds.
900 .BR -f ", " --daemonise
903 to run as a background daemon if it decides to monitor anything. This
904 causes it to fork and run in the child, and to disconnect form the
905 terminal. The process id of the child is written to stdout.
908 which will only continue monitoring if a mail address or alert program
909 is found in the config file.
912 .BR -i ", " --pid-file
915 is running in daemon mode, write the pid of the daemon process to
916 the specified file, instead of printing it on standard output.
919 .BR -1 ", " --oneshot
920 Check arrays only once. This will generate
922 events and more significantly
928 .B " mdadm --monitor --scan -1"
930 from a cron script will ensure regular notification of any degraded arrays.
936 alert for every array found at startup. This alert gets mailed and
937 passed to the alert program. This can be used for testing that alert
938 message do get through successfully.
945 .I md-device options-and-component-devices...
948 .B mdadm --assemble --scan
949 .I md-devices-and-options...
952 .B mdadm --assemble --scan
956 This usage assembles one or more raid arrays from pre-existing components.
957 For each array, mdadm needs to know the md device, the identity of the
958 array, and a number of component-devices. These can be found in a number of ways.
960 In the first usage example (without the
962 the first device given is the md device.
963 In the second usage example, all devices listed are treated as md
964 devices and assembly is attempted.
965 In the third (where no devices are listed) all md devices that are
966 listed in the configuration file are assembled.
968 If precisely one device is listed, but
974 was given and identify information is extracted from the configuration file.
976 The identity can be given with the
980 option, can be found in the config file, or will be taken from the
981 super block on the first component-device listed on the command line.
983 Devices can be given on the
985 command line or in the config file. Only devices which have an md
986 superblock which contains the right identity will be considered for
989 The config file is only used if explicitly named with
991 or requested with (a possibly implicit)
999 is not given, then the config file will only be used to find the
1000 identity of md arrays.
1002 Normally the array will be started after it is assembled. However if
1004 is not given and insufficient drives were listed to start a complete
1005 (non-degraded) array, then the array is not started (to guard against
1006 usage errors). To insist that the array be started in this case (as
1007 may work for RAID1, 4, 5, 6, or 10), give the
1013 option is given, either on the command line (--auto) or in the
1014 configuration file (e.g. auto=part), then
1016 will create the md device if necessary or will re-create it if it
1017 doesn't look usable as it is.
1019 This can be useful for handling partitioned devices (which don't have
1020 a stable device number - it can change after a reboot) and when using
1021 "udev" to manage your
1023 tree (udev cannot handle md devices because of the unusual device
1024 initialisation conventions).
1026 If the option to "auto" is "mdp" or "part" or (on the command line
1027 only) "p", then mdadm will create a partitionable array, using the
1028 first free one that is not in use, and does not already have an entry
1029 in /dev (apart from numeric /dev/md* entries).
1031 If the option to "auto" is "yes" or "md" or (on the command line)
1032 nothing, then mdadm will create a traditional, non-partitionable md
1035 It is expected that the "auto" functionality will be used to create
1036 device entries with meaningful names such as "/dev/md/home" or
1037 "/dev/md/root", rather than names based on the numerical array number.
1039 When using this option to create a partitionable array, the device
1040 files for the first 4 partitions are also created. If a different
1041 number is required it can be simply appended to the auto option.
1042 e.g. "auto=part8". Partition names are created by appending a digit
1043 string to the device name, with an intervening "p" if the device name
1048 option is also available in Build and Create modes. As those modes do
1049 not use a config file, the "auto=" config option does not apply to
1057 and no devices are listed,
1059 will first attempt to assemble all the arrays listed in the config
1064 has been specified (either in the config file or on the command line),
1066 will look further for possible arrays and will try to assemble
1067 anything that it finds which is tagged as belonging to the given
1068 homehost. This is the only situation where
1070 will assemble arrays without being given specific device name or
1071 identify information for the array.
1075 finds a consistent set of devices that look like they should comprise
1076 an array, and if the superblock is tagged as belonging to the given
1077 home host, it will automatically choose a device name and try to
1078 assemble the array. If the array uses version-0.90 metadata, then the
1080 number as recorded in the superblock is used to create a name in
1084 If the array uses version-1 metadata, then the
1086 from the superblock is used to similarly create a name in
1088 The name will have any 'host' prefix stripped first.
1092 cannot find any array for the given host at all, and if
1093 .B --auto-update-homehost
1096 will search again for any array (not just an array created for this
1097 host) and will assemble each assuming
1098 .IR --update=homehost .
1099 This will change the host tag in the superblock so that on the next run,
1100 these arrays will be found without the second pass. The intention of
1101 this feature is to support transitioning a set of md arrays to using
1104 The reason for requiring arrays to be tagged with the homehost for
1105 auto assembly is to guard against problems that can arise when moving
1106 devices from one host to another.
1116 .BI --raid-devices= Z
1120 This usage is similar to
1122 The difference is that it creates an array without a superblock. With
1123 these arrays there is no difference between initially creating the array and
1124 subsequently assembling the array, except that hopefully there is useful
1125 data there in the second case.
1127 The level may raid0, linear, multipath, or faulty, or one of their
1128 synonyms. All devices must be listed and the array will be started
1140 .BI --raid-devices= Z
1144 This usage will initialise a new md array, associate some devices with
1145 it, and activate the array.
1149 option is given (as described in more detail in the section on
1150 Assemble mode), then the md device will be created with a suitable
1151 device number if necessary.
1153 As devices are added, they are checked to see if they contain raid
1154 superblocks or filesystems. They are also checked to see if the variance in
1155 device size exceeds 1%.
1157 If any discrepancy is found, the array will not automatically be run, though
1160 can override this caution.
1162 To create a "degraded" array in which some devices are missing, simply
1163 give the word "\fBmissing\fP"
1164 in place of a device name. This will cause
1166 to leave the corresponding slot in the array empty.
1167 For a RAID4 or RAID5 array at most one slot can be
1168 "\fBmissing\fP"; for a RAID6 array at most two slots.
1169 For a RAID1 array, only one real device needs to be given. All of the
1173 When creating a RAID5 array,
1175 will automatically create a degraded array with an extra spare drive.
1176 This is because building the spare into a degraded array is in general faster than resyncing
1177 the parity on a non-degraded, but not clean, array. This feature can
1178 be over-ridden with the
1182 When creating an array with version-1 metadata a name for the host is
1184 If this is not given with the
1188 will chose a name based on the last component of the name of the
1189 device being created. So if
1191 is being created, then the name
1196 is being created, then the name
1202 '''option is given, it is not necessary to list any component-devices in this command.
1203 '''They can be added later, before a
1207 '''is given, the apparent size of the smallest drive given is used.
1209 The General Management options that are valid with --create are:
1212 insist on running the array even if some devices look like they might
1217 start the array readonly - not supported yet.
1225 .I options... devices...
1228 This usage will allow individual devices in an array to be failed,
1229 removed or added. It is possible to perform multiple operations with
1230 on command. For example:
1232 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1238 and will then remove it from the array and finally add it back
1239 in as a spare. However only one md array can be affected by a single
1250 MISC mode includes a number of distinct operations that
1251 operate on distinct devices. The operations are:
1254 The device is examined to see if it is
1255 (1) an active md array, or
1256 (2) a component of an md array.
1257 The information discovered is reported.
1261 The device should be an active md device.
1263 will display a detailed description of the array.
1267 will cause the output to be less detailed and the format to be
1268 suitable for inclusion in
1269 .BR /etc/mdadm.conf .
1272 will normally be 0 unless
1274 failed to get useful information about the device(s). However if the
1276 option is given, then the exit status will be:
1280 The array is functioning normally.
1283 The array has at least one failed device.
1286 The array has multiple failed devices and hence is unusable (raid4 or
1290 There was an error while trying to get information about the device.
1295 The device should be a component of an md array.
1297 will read the md superblock of the device and display the contents.
1302 then multiple devices that are components of the one array
1303 are grouped together and reported in a single entry suitable
1305 .BR /etc/mdadm.conf .
1309 without listing any devices will cause all devices listed in the
1310 config file to be examined.
1314 The devices should be active md arrays which will be deactivated, as
1315 long as they are not currently in use.
1319 This will fully activate a partially assembled md array.
1323 This will mark an active array as read-only, providing that it is
1324 not currently being used.
1330 array back to being read/write.
1334 For all operations except
1337 will cause the operation to be applied to all arrays listed in
1342 causes all devices listed in the config file to be examined.
1350 .I options... devices...
1355 to periodically poll a number of md arrays and to report on any events
1358 will never exit once it decides that there are arrays to be checked,
1359 so it should normally be run in the background.
1361 As well as reporting events,
1363 may move a spare drive from one array to another if they are in the
1366 and if the destination array has a failed drive but no spares.
1368 If any devices are listed on the command line,
1370 will only monitor those devices. Otherwise all arrays listed in the
1371 configuration file will be monitored. Further, if
1373 is given, then any other md devices that appear in
1375 will also be monitored.
1377 The result of monitoring the arrays is the generation of events.
1378 These events are passed to a separate program (if specified) and may
1379 be mailed to a given E-mail address.
1381 When passing event to program, the program is run once for each event
1382 and is given 2 or 3 command-line arguments. The first is the
1383 name of the event (see below). The second is the name of the
1384 md device which is affected, and the third is the name of a related
1385 device if relevant, such as a component device that has failed.
1389 is given, then a program or an E-mail address must be specified on the
1390 command line or in the config file. If neither are available, then
1392 will not monitor anything.
1396 will continue monitoring as long as something was found to monitor. If
1397 no program or email is given, then each event is reported to
1400 The different events are:
1404 .B DeviceDisappeared
1405 An md array which previously was configured appears to no longer be
1406 configured. (syslog priority: Critical)
1410 was told to monitor an array which is RAID0 or Linear, then it will
1412 .B DeviceDisappeared
1413 with the extra information
1415 This is because RAID0 and Linear do not support the device-failed,
1416 hot-spare and resync operations which are monitored.
1420 An md array started reconstruction. (syslog priority: Warning)
1426 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1427 percentage of the total. (syslog priority: Warning)
1431 An md array that was rebuilding, isn't any more, either because it
1432 finished normally or was aborted. (syslog priority: Warning)
1436 An active component device of an array has been marked as
1437 faulty. (syslog priority: Critical)
1441 A spare component device which was being rebuilt to replace a faulty
1442 device has failed. (syslog priority: Critial)
1446 A spare component device which was being rebuilt to replace a faulty
1447 device has been successfully rebuilt and has been made active.
1448 (syslog priority: Info)
1452 A new md array has been detected in the
1454 file. (syslog priority: Info)
1458 A newly noticed array appears to be degraded. This message is not
1461 notices a drive failure which causes degradation, but only when
1463 notices that an array is degraded when it first sees the array.
1464 (syslog priority: Critial)
1468 A spare drive has been moved from one array in a
1470 to another to allow a failed drive to be replaced.
1471 (syslog priority: Info)
1477 has been told, via the config file, that an array should have a certain
1478 number of spare devices, and
1480 detects that it has fewer that this number when it first sees the
1481 array, it will report a
1484 (syslog priority: Warning)
1488 An array was found at startup, and the
1491 (syslog priority: Info)
1501 cause Email to be sent. All events cause the program to be run.
1502 The program is run with two or three arguments, they being the event
1503 name, the array device and possibly a second device.
1505 Each event has an associated array device (e.g.
1507 and possibly a second device. For
1512 the second device is the relevant component device.
1515 the second device is the array that the spare was moved from.
1519 to move spares from one array to another, the different arrays need to
1520 be labelled with the same
1522 in the configuration file. The
1524 name can be any string. It is only necessary that different spare
1525 groups use different names.
1529 detects that an array which is in a spare group has fewer active
1530 devices than necessary for the complete array, and has no spare
1531 devices, it will look for another array in the same spare group that
1532 has a full complement of working drive and a spare. It will then
1533 attempt to remove the spare from the second drive and add it to the
1535 If the removal succeeds but the adding fails, then it is added back to
1539 The GROW mode is used for changing the size or shape of an active
1541 For this to work, the kernel must support the necessary change.
1542 Various types of growth are being added during 2.6 development,
1543 including restructuring a raid5 array to have more active devices.
1545 Currently the only support available is to
1547 change the "size" attribute
1548 for RAID1, RAID5 and RAID6.
1550 increase the "raid-disks" attribute of RAID1 and RAID5.
1552 add a write-intent bitmap to any array which support these bitmaps, or
1553 remove a write-intent bitmap from such an array.
1557 Normally when an array is built the "size" it taken from the smallest
1558 of the drives. If all the small drives in an arrays are, one at a
1559 time, removed and replaced with larger drives, then you could have an
1560 array of large drives with only a small amount used. In this
1561 situation, changing the "size" with "GROW" mode will allow the extra
1562 space to start being used. If the size is increased in this way, a
1563 "resync" process will start to make sure the new parts of the array
1566 Note that when an array changes size, any filesystem that may be
1567 stored in the array will not automatically grow to use the space. The
1568 filesystem will need to be explicitly told to use the extra space.
1570 .SS RAID-DEVICES CHANGES
1572 A RAID1 array can work with any number of devices from 1 upwards
1573 (though 1 is not very useful). There may be times which you want to
1574 increase or decrease the number of active devices. Note that this is
1575 different to hot-add or hot-remove which changes the number of
1578 When reducing the number of devices in a RAID1 array, the slots which
1579 are to be removed from the array must already be vacant. That is, the
1580 devices that which were in those slots must be failed and removed.
1582 When the number of devices is increased, any hot spares that are
1583 present will be activated immediately.
1585 Increasing the number of active devices in a RAID5 is much more
1586 effort. Every block in the array will need to be read and written
1587 back to a new location. From 2.6.17, the Linux Kernel is able to do
1588 this safely, including restart and interrupted "reshape".
1590 When relocating the first few stripes on a raid5, it is not possible
1591 to keep the data on disk completely consistent and crash-proof. To
1592 provide the required safety, mdadm disables writes to the array while
1593 this "critical section" is reshaped, and takes a backup of the data
1594 that is in that section. This backup is normally stored in any spare
1595 devices that the array has, however it can also be stored in a
1596 separate file specified with the
1598 option. If this option is used, and the system does crash during the
1599 critical period, the same file must be passed to
1601 to restore the backup and reassemble the array.
1605 A write-intent bitmap can be added to, or removed from, an active
1606 array. Either internal bitmaps, or bitmaps stored in a separate file
1607 can be added. Note that if you add a bitmap stored in a file which is
1608 in a filesystem that is on the raid array being affected, the system
1609 will deadlock. The bitmap must be on a separate filesystem.
1613 .B " mdadm --query /dev/name-of-device"
1615 This will find out if a given device is a raid array, or is part of
1616 one, and will provide brief information about the device.
1618 .B " mdadm --assemble --scan"
1620 This will assemble and start all arrays listed in the standard config file
1621 file. This command will typically go in a system startup file.
1623 .B " mdadm --stop --scan"
1625 This will shut down all array that can be shut down (i.e. are not
1626 currently in use). This will typically go in a system shutdown script.
1628 .B " mdadm --follow --scan --delay=120"
1630 If (and only if) there is an Email address or program given in the
1631 standard config file, then
1632 monitor the status of all arrays listed in that file by
1633 polling them ever 2 minutes.
1635 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1637 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1640 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1642 .B " mdadm --detail --scan >> mdadm.conf"
1644 This will create a prototype config file that describes currently
1645 active arrays that are known to be made from partitions of IDE or SCSI drives.
1646 This file should be reviewed before being used as it may
1647 contain unwanted detail.
1649 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1651 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1653 This will find what arrays could be assembled from existing IDE and
1654 SCSI whole drives (not partitions) and store the information is the
1655 format of a config file.
1656 This file is very likely to contain unwanted detail, particularly
1659 entries. It should be reviewed and edited before being used as an
1662 .B " mdadm --examine --brief --scan --config=partitions"
1664 .B " mdadm -Ebsc partitions"
1666 Create a list of devices by reading
1667 .BR /proc/partitions ,
1668 scan these for RAID superblocks, and printout a brief listing of all
1671 .B " mdadm -Ac partitions -m 0 /dev/md0"
1673 Scan all partitions and devices listed in
1674 .BR /proc/partitions
1677 out of all such devices with a RAID superblock with a minor number of 0.
1679 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1681 If config file contains a mail address or alert program, run mdadm in
1682 the background in monitor mode monitoring all md devices. Also write
1683 pid of mdadm daemon to
1684 .BR /var/run/mdadm .
1686 .B " mdadm --create --help"
1688 Provide help about the Create mode.
1690 .B " mdadm --config --help"
1692 Provide help about the format of the config file.
1696 Provide general help.
1707 lists all active md devices with information about them.
1709 uses this to find arrays when
1711 is given in Misc mode, and to monitor array reconstruction
1717 The config file lists which devices may be scanned to see if
1718 they contain MD super block, and gives identifying information
1719 (e.g. UUID) about known MD arrays. See
1725 While entries in the /dev directory can have any format you like,
1727 has an understanding of 'standard' formats which it uses to guide its
1728 behaviour when creating device files via the
1732 The standard names for non-partitioned arrays (the only sort of md
1733 array available in 2.4 and earlier) either of
1739 where NN is a number.
1740 The standard names for partitionable arrays (as available from 2.6
1747 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1751 was previously known as
1755 is completely separate from the
1757 package, and does not use the
1759 configuration file at all.
1762 For information on the various levels of
1766 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1767 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1770 '''for new releases of the RAID driver check out:
1773 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1774 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1779 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1780 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1783 The latest version of
1785 should always be available from
1787 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1788 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob