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
605 it will also create symlinks from
607 with names starting with
615 to enforce this even if it is suppressing
623 uuid of array to assemble. Devices which don't have this uuid are
627 .BR -m ", " --super-minor=
628 Minor number of device that array was created for. Devices which
629 don't have this minor number are excluded. If you create an array as
630 /dev/md1, then all superblocks will contain the minor number 1, even if
631 the array is later assembled as /dev/md2.
633 Giving the literal word "dev" for
637 to use the minor number of the md device that is being assembled.
641 will look for super blocks with a minor number of 0.
645 Specify the name of the array to assemble. This must be the name
646 that was specified when creating the array. It must either match
647 then name stored in the superblock exactly, or it must match
650 is added to the start of the given name.
654 Assemble the array even if some superblocks appear out-of-date
658 Attempt to start the array even if fewer drives were given than were
659 present last time the array was active. Normally if not all the
660 expected drives are found and
662 is not used, then the array will be assembled but not started.
665 an attempt will be made to start it anyway.
669 This is the reverse of
671 in that it inhibits the started if array unless all expected drives
672 are present. This is only needed with
674 and can be used if you physical connections to devices are
675 not as reliable as you would like.
678 .BR -a ", " "--auto{=no,yes,md,mdp,part}"
679 See this option under Create and Build options.
682 .BR -b ", " --bitmap=
683 Specify the bitmap file that was given when the array was created. If
686 bitmap, there is no need to specify this when assembling the array.
692 was used to grow the number of raid-devices in a RAID5, and the system
693 crashed during the critical section, then the same
695 must be presented to --assemble to allow possibly corrupted data to be
699 .BR -U ", " --update=
700 Update the superblock on each device while assembling the array. The
701 argument given to this flag can be one of
714 option will adjust the superblock of an array what was created on a Sparc
715 machine running a patched 2.2 Linux kernel. This kernel got the
716 alignment of part of the superblock wrong. You can use the
717 .B "--examine --sparc2.2"
720 to see what effect this would have.
724 option will update the
726 field on each superblock to match the minor number of the array being
727 assembled. This is not needed on 2.6 and later kernels as they make
728 this adjustment automatically.
732 option will change the uuid of the array. If a UUID is given with the
733 "--uuid" option that UUID will be used as a new UUID and will
735 be used to help identify the devices in the array.
736 If no "--uuid" is given, a random uuid is chosen.
740 option will change the
742 of the array as stored in the superblock. This is only supported for
743 version-1 superblocks.
747 option will change the
749 as recorded in the superblock. For version-0 superblocks, this is the
750 same as updating the UUID.
751 For version-1 superblocks, this involves updating the name.
755 option will cause the array to be marked
757 meaning that any redundancy in the array (e.g. parity for raid5,
758 copies for raid1) may be incorrect. This will cause the raid system
759 to perform a "resync" pass to make sure that all redundant information
764 option allows arrays to be moved between machines with different
766 When assembling such an array for the first time after a move, giving
767 .B "--update=byteorder"
770 to expect superblocks to have their byteorder reversed, and will
771 correct that order before assembling the array. This is only valid
772 with original (Version 0.90) superblocks.
776 option will correct the summaries in the superblock. That is the
777 counts of total, working, active, failed, and spare devices.
780 .B --auto-update-homehost
781 This flag is only meaning with auto-assembly (see discussion below).
782 In that situation, if no suitable arrays are found for this homehost,
784 will recan for any arrays at all and will assemble them and update the
785 homehost to match the current host.
791 hot-add listed devices.
795 re-add a device that was recently removed from an array.
799 remove listed devices. They must not be active. i.e. they should
800 be failed or spare devices.
804 mark listed devices as faulty.
811 Each of these options require that the first device list is the array
812 to be acted upon and the remainder are component devices to be added,
813 removed, or marked as fault. Several different operations can be
814 specified for different devices, e.g.
816 mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
818 Each operation applies to all devices listed until the next
821 If an array is using a write-intent bitmap, then devices which have
822 been removed can be re-added in a way that avoids a full
823 reconstruction but instead just updated the blocks that have changed
824 since the device was removed. For arrays with persistent metadata
825 (superblocks) this is done automatically. For arrays created with
827 mdadm needs to be told that this device we removed recently with
830 Devices can only be removed from an array if they are not in active
831 use. i.e. that must be spares or failed devices. To remove an active
832 device, it must be marked as
840 Examine a device to see
841 (1) if it is an md device and (2) if it is a component of an md
843 Information about what is discovered is presented.
847 Print detail of one or more md devices.
850 .BR -E ", " --examine
851 Print content of md superblock on device(s).
854 If an array was created on a 2.2 Linux kernel patched with RAID
855 support, the superblock will have been created incorrectly, or at
856 least incompatibly with 2.4 and later kernels. Using the
860 will fix the superblock before displaying it. If this appears to do
861 the right thing, then the array can be successfully assembled using
862 .BR "--assemble --update=sparc2.2" .
865 .BR -X ", " --examine-bitmap
866 Report information about a bitmap file.
870 start a partially built array.
874 deactivate array, releasing all resources.
877 .BR -o ", " --readonly
878 mark array as readonly.
881 .BR -w ", " --readwrite
882 mark array as readwrite.
886 If the device contains a valid md superblock, the block is
887 over-written with zeros. With
889 the block where the superblock would be is over-written even if it
890 doesn't appear to be valid.
898 is set to reflect the status of the device.
900 .SH For Monitor mode:
903 Give a mail address to send alerts to.
906 .BR -p ", " --program ", " --alert
907 Give a program to be run whenever an event is detected.
911 Cause all events to be reported through 'syslog'. The messages have
912 facility of 'daemon' and varying priorities.
916 Give a delay in seconds.
918 polls the md arrays and then waits this many seconds before polling
919 again. The default is 60 seconds.
922 .BR -f ", " --daemonise
925 to run as a background daemon if it decides to monitor anything. This
926 causes it to fork and run in the child, and to disconnect form the
927 terminal. The process id of the child is written to stdout.
930 which will only continue monitoring if a mail address or alert program
931 is found in the config file.
934 .BR -i ", " --pid-file
937 is running in daemon mode, write the pid of the daemon process to
938 the specified file, instead of printing it on standard output.
941 .BR -1 ", " --oneshot
942 Check arrays only once. This will generate
944 events and more significantly
950 .B " mdadm --monitor --scan -1"
952 from a cron script will ensure regular notification of any degraded arrays.
958 alert for every array found at startup. This alert gets mailed and
959 passed to the alert program. This can be used for testing that alert
960 message do get through successfully.
967 .I md-device options-and-component-devices...
970 .B mdadm --assemble --scan
971 .I md-devices-and-options...
974 .B mdadm --assemble --scan
978 This usage assembles one or more raid arrays from pre-existing components.
979 For each array, mdadm needs to know the md device, the identity of the
980 array, and a number of component-devices. These can be found in a number of ways.
982 In the first usage example (without the
984 the first device given is the md device.
985 In the second usage example, all devices listed are treated as md
986 devices and assembly is attempted.
987 In the third (where no devices are listed) all md devices that are
988 listed in the configuration file are assembled.
990 If precisely one device is listed, but
996 was given and identify information is extracted from the configuration file.
998 The identity can be given with the
1002 option, can be found in the config file, or will be taken from the
1003 super block on the first component-device listed on the command line.
1005 Devices can be given on the
1007 command line or in the config file. Only devices which have an md
1008 superblock which contains the right identity will be considered for
1011 The config file is only used if explicitly named with
1013 or requested with (a possibly implicit)
1021 is not given, then the config file will only be used to find the
1022 identity of md arrays.
1024 Normally the array will be started after it is assembled. However if
1026 is not given and insufficient drives were listed to start a complete
1027 (non-degraded) array, then the array is not started (to guard against
1028 usage errors). To insist that the array be started in this case (as
1029 may work for RAID1, 4, 5, 6, or 10), give the
1035 option is given, either on the command line (--auto) or in the
1036 configuration file (e.g. auto=part), then
1038 will create the md device if necessary or will re-create it if it
1039 doesn't look usable as it is.
1041 This can be useful for handling partitioned devices (which don't have
1042 a stable device number - it can change after a reboot) and when using
1043 "udev" to manage your
1045 tree (udev cannot handle md devices because of the unusual device
1046 initialisation conventions).
1048 If the option to "auto" is "mdp" or "part" or (on the command line
1049 only) "p", then mdadm will create a partitionable array, using the
1050 first free one that is not in use, and does not already have an entry
1051 in /dev (apart from numeric /dev/md* entries).
1053 If the option to "auto" is "yes" or "md" or (on the command line)
1054 nothing, then mdadm will create a traditional, non-partitionable md
1057 It is expected that the "auto" functionality will be used to create
1058 device entries with meaningful names such as "/dev/md/home" or
1059 "/dev/md/root", rather than names based on the numerical array number.
1061 When using this option to create a partitionable array, the device
1062 files for the first 4 partitions are also created. If a different
1063 number is required it can be simply appended to the auto option.
1064 e.g. "auto=part8". Partition names are created by appending a digit
1065 string to the device name, with an intervening "p" if the device name
1070 option is also available in Build and Create modes. As those modes do
1071 not use a config file, the "auto=" config option does not apply to
1079 and no devices are listed,
1081 will first attempt to assemble all the arrays listed in the config
1086 has been specified (either in the config file or on the command line),
1088 will look further for possible arrays and will try to assemble
1089 anything that it finds which is tagged as belonging to the given
1090 homehost. This is the only situation where
1092 will assemble arrays without being given specific device name or
1093 identify information for the array.
1097 finds a consistent set of devices that look like they should comprise
1098 an array, and if the superblock is tagged as belonging to the given
1099 home host, it will automatically choose a device name and try to
1100 assemble the array. If the array uses version-0.90 metadata, then the
1102 number as recorded in the superblock is used to create a name in
1106 If the array uses version-1 metadata, then the
1108 from the superblock is used to similarly create a name in
1110 The name will have any 'host' prefix stripped first.
1114 cannot find any array for the given host at all, and if
1115 .B --auto-update-homehost
1118 will search again for any array (not just an array created for this
1119 host) and will assemble each assuming
1120 .IR --update=homehost .
1121 This will change the host tag in the superblock so that on the next run,
1122 these arrays will be found without the second pass. The intention of
1123 this feature is to support transitioning a set of md arrays to using
1126 The reason for requiring arrays to be tagged with the homehost for
1127 auto assembly is to guard against problems that can arise when moving
1128 devices from one host to another.
1138 .BI --raid-devices= Z
1142 This usage is similar to
1144 The difference is that it creates an array without a superblock. With
1145 these arrays there is no difference between initially creating the array and
1146 subsequently assembling the array, except that hopefully there is useful
1147 data there in the second case.
1149 The level may raid0, linear, multipath, or faulty, or one of their
1150 synonyms. All devices must be listed and the array will be started
1162 .BI --raid-devices= Z
1166 This usage will initialise a new md array, associate some devices with
1167 it, and activate the array.
1171 option is given (as described in more detail in the section on
1172 Assemble mode), then the md device will be created with a suitable
1173 device number if necessary.
1175 As devices are added, they are checked to see if they contain raid
1176 superblocks or filesystems. They are also checked to see if the variance in
1177 device size exceeds 1%.
1179 If any discrepancy is found, the array will not automatically be run, though
1182 can override this caution.
1184 To create a "degraded" array in which some devices are missing, simply
1185 give the word "\fBmissing\fP"
1186 in place of a device name. This will cause
1188 to leave the corresponding slot in the array empty.
1189 For a RAID4 or RAID5 array at most one slot can be
1190 "\fBmissing\fP"; for a RAID6 array at most two slots.
1191 For a RAID1 array, only one real device needs to be given. All of the
1195 When creating a RAID5 array,
1197 will automatically create a degraded array with an extra spare drive.
1198 This is because building the spare into a degraded array is in general faster than resyncing
1199 the parity on a non-degraded, but not clean, array. This feature can
1200 be over-ridden with the
1204 When creating an array with version-1 metadata a name for the host is
1206 If this is not given with the
1210 will chose a name based on the last component of the name of the
1211 device being created. So if
1213 is being created, then the name
1218 is being created, then the name
1224 '''option is given, it is not necessary to list any component-devices in this command.
1225 '''They can be added later, before a
1229 '''is given, the apparent size of the smallest drive given is used.
1231 The General Management options that are valid with --create are:
1234 insist on running the array even if some devices look like they might
1239 start the array readonly - not supported yet.
1247 .I options... devices...
1250 This usage will allow individual devices in an array to be failed,
1251 removed or added. It is possible to perform multiple operations with
1252 on command. For example:
1254 .B " mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1"
1260 and will then remove it from the array and finally add it back
1261 in as a spare. However only one md array can be affected by a single
1272 MISC mode includes a number of distinct operations that
1273 operate on distinct devices. The operations are:
1276 The device is examined to see if it is
1277 (1) an active md array, or
1278 (2) a component of an md array.
1279 The information discovered is reported.
1283 The device should be an active md device.
1285 will display a detailed description of the array.
1289 will cause the output to be less detailed and the format to be
1290 suitable for inclusion in
1291 .BR /etc/mdadm.conf .
1294 will normally be 0 unless
1296 failed to get useful information about the device(s). However if the
1298 option is given, then the exit status will be:
1302 The array is functioning normally.
1305 The array has at least one failed device.
1308 The array has multiple failed devices and hence is unusable (raid4 or
1312 There was an error while trying to get information about the device.
1317 The device should be a component of an md array.
1319 will read the md superblock of the device and display the contents.
1324 then multiple devices that are components of the one array
1325 are grouped together and reported in a single entry suitable
1327 .BR /etc/mdadm.conf .
1331 without listing any devices will cause all devices listed in the
1332 config file to be examined.
1336 The devices should be active md arrays which will be deactivated, as
1337 long as they are not currently in use.
1341 This will fully activate a partially assembled md array.
1345 This will mark an active array as read-only, providing that it is
1346 not currently being used.
1352 array back to being read/write.
1356 For all operations except
1359 will cause the operation to be applied to all arrays listed in
1364 causes all devices listed in the config file to be examined.
1372 .I options... devices...
1377 to periodically poll a number of md arrays and to report on any events
1380 will never exit once it decides that there are arrays to be checked,
1381 so it should normally be run in the background.
1383 As well as reporting events,
1385 may move a spare drive from one array to another if they are in the
1388 and if the destination array has a failed drive but no spares.
1390 If any devices are listed on the command line,
1392 will only monitor those devices. Otherwise all arrays listed in the
1393 configuration file will be monitored. Further, if
1395 is given, then any other md devices that appear in
1397 will also be monitored.
1399 The result of monitoring the arrays is the generation of events.
1400 These events are passed to a separate program (if specified) and may
1401 be mailed to a given E-mail address.
1403 When passing event to program, the program is run once for each event
1404 and is given 2 or 3 command-line arguments. The first is the
1405 name of the event (see below). The second is the name of the
1406 md device which is affected, and the third is the name of a related
1407 device if relevant, such as a component device that has failed.
1411 is given, then a program or an E-mail address must be specified on the
1412 command line or in the config file. If neither are available, then
1414 will not monitor anything.
1418 will continue monitoring as long as something was found to monitor. If
1419 no program or email is given, then each event is reported to
1422 The different events are:
1426 .B DeviceDisappeared
1427 An md array which previously was configured appears to no longer be
1428 configured. (syslog priority: Critical)
1432 was told to monitor an array which is RAID0 or Linear, then it will
1434 .B DeviceDisappeared
1435 with the extra information
1437 This is because RAID0 and Linear do not support the device-failed,
1438 hot-spare and resync operations which are monitored.
1442 An md array started reconstruction. (syslog priority: Warning)
1448 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1449 percentage of the total. (syslog priority: Warning)
1453 An md array that was rebuilding, isn't any more, either because it
1454 finished normally or was aborted. (syslog priority: Warning)
1458 An active component device of an array has been marked as
1459 faulty. (syslog priority: Critical)
1463 A spare component device which was being rebuilt to replace a faulty
1464 device has failed. (syslog priority: Critial)
1468 A spare component device which was being rebuilt to replace a faulty
1469 device has been successfully rebuilt and has been made active.
1470 (syslog priority: Info)
1474 A new md array has been detected in the
1476 file. (syslog priority: Info)
1480 A newly noticed array appears to be degraded. This message is not
1483 notices a drive failure which causes degradation, but only when
1485 notices that an array is degraded when it first sees the array.
1486 (syslog priority: Critial)
1490 A spare drive has been moved from one array in a
1492 to another to allow a failed drive to be replaced.
1493 (syslog priority: Info)
1499 has been told, via the config file, that an array should have a certain
1500 number of spare devices, and
1502 detects that it has fewer that this number when it first sees the
1503 array, it will report a
1506 (syslog priority: Warning)
1510 An array was found at startup, and the
1513 (syslog priority: Info)
1523 cause Email to be sent. All events cause the program to be run.
1524 The program is run with two or three arguments, they being the event
1525 name, the array device and possibly a second device.
1527 Each event has an associated array device (e.g.
1529 and possibly a second device. For
1534 the second device is the relevant component device.
1537 the second device is the array that the spare was moved from.
1541 to move spares from one array to another, the different arrays need to
1542 be labelled with the same
1544 in the configuration file. The
1546 name can be any string. It is only necessary that different spare
1547 groups use different names.
1551 detects that an array which is in a spare group has fewer active
1552 devices than necessary for the complete array, and has no spare
1553 devices, it will look for another array in the same spare group that
1554 has a full complement of working drive and a spare. It will then
1555 attempt to remove the spare from the second drive and add it to the
1557 If the removal succeeds but the adding fails, then it is added back to
1561 The GROW mode is used for changing the size or shape of an active
1563 For this to work, the kernel must support the necessary change.
1564 Various types of growth are being added during 2.6 development,
1565 including restructuring a raid5 array to have more active devices.
1567 Currently the only support available is to
1569 change the "size" attribute
1570 for RAID1, RAID5 and RAID6.
1572 increase the "raid-disks" attribute of RAID1 and RAID5.
1574 add a write-intent bitmap to any array which support these bitmaps, or
1575 remove a write-intent bitmap from such an array.
1579 Normally when an array is built the "size" it taken from the smallest
1580 of the drives. If all the small drives in an arrays are, one at a
1581 time, removed and replaced with larger drives, then you could have an
1582 array of large drives with only a small amount used. In this
1583 situation, changing the "size" with "GROW" mode will allow the extra
1584 space to start being used. If the size is increased in this way, a
1585 "resync" process will start to make sure the new parts of the array
1588 Note that when an array changes size, any filesystem that may be
1589 stored in the array will not automatically grow to use the space. The
1590 filesystem will need to be explicitly told to use the extra space.
1592 .SS RAID-DEVICES CHANGES
1594 A RAID1 array can work with any number of devices from 1 upwards
1595 (though 1 is not very useful). There may be times which you want to
1596 increase or decrease the number of active devices. Note that this is
1597 different to hot-add or hot-remove which changes the number of
1600 When reducing the number of devices in a RAID1 array, the slots which
1601 are to be removed from the array must already be vacant. That is, the
1602 devices that which were in those slots must be failed and removed.
1604 When the number of devices is increased, any hot spares that are
1605 present will be activated immediately.
1607 Increasing the number of active devices in a RAID5 is much more
1608 effort. Every block in the array will need to be read and written
1609 back to a new location. From 2.6.17, the Linux Kernel is able to do
1610 this safely, including restart and interrupted "reshape".
1612 When relocating the first few stripes on a raid5, it is not possible
1613 to keep the data on disk completely consistent and crash-proof. To
1614 provide the required safety, mdadm disables writes to the array while
1615 this "critical section" is reshaped, and takes a backup of the data
1616 that is in that section. This backup is normally stored in any spare
1617 devices that the array has, however it can also be stored in a
1618 separate file specified with the
1620 option. If this option is used, and the system does crash during the
1621 critical period, the same file must be passed to
1623 to restore the backup and reassemble the array.
1627 A write-intent bitmap can be added to, or removed from, an active
1628 array. Either internal bitmaps, or bitmaps stored in a separate file
1629 can be added. Note that if you add a bitmap stored in a file which is
1630 in a filesystem that is on the raid array being affected, the system
1631 will deadlock. The bitmap must be on a separate filesystem.
1635 .B " mdadm --query /dev/name-of-device"
1637 This will find out if a given device is a raid array, or is part of
1638 one, and will provide brief information about the device.
1640 .B " mdadm --assemble --scan"
1642 This will assemble and start all arrays listed in the standard config file
1643 file. This command will typically go in a system startup file.
1645 .B " mdadm --stop --scan"
1647 This will shut down all array that can be shut down (i.e. are not
1648 currently in use). This will typically go in a system shutdown script.
1650 .B " mdadm --follow --scan --delay=120"
1652 If (and only if) there is an Email address or program given in the
1653 standard config file, then
1654 monitor the status of all arrays listed in that file by
1655 polling them ever 2 minutes.
1657 .B " mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1"
1659 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
1662 .B " echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf"
1664 .B " mdadm --detail --scan >> mdadm.conf"
1666 This will create a prototype config file that describes currently
1667 active arrays that are known to be made from partitions of IDE or SCSI drives.
1668 This file should be reviewed before being used as it may
1669 contain unwanted detail.
1671 .B " echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf"
1673 .B " mdadm --examine --scan --config=mdadm.conf >> mdadm.conf"
1675 This will find what arrays could be assembled from existing IDE and
1676 SCSI whole drives (not partitions) and store the information is the
1677 format of a config file.
1678 This file is very likely to contain unwanted detail, particularly
1681 entries. It should be reviewed and edited before being used as an
1684 .B " mdadm --examine --brief --scan --config=partitions"
1686 .B " mdadm -Ebsc partitions"
1688 Create a list of devices by reading
1689 .BR /proc/partitions ,
1690 scan these for RAID superblocks, and printout a brief listing of all
1693 .B " mdadm -Ac partitions -m 0 /dev/md0"
1695 Scan all partitions and devices listed in
1696 .BR /proc/partitions
1699 out of all such devices with a RAID superblock with a minor number of 0.
1701 .B " mdadm --monitor --scan --daemonise > /var/run/mdadm"
1703 If config file contains a mail address or alert program, run mdadm in
1704 the background in monitor mode monitoring all md devices. Also write
1705 pid of mdadm daemon to
1706 .BR /var/run/mdadm .
1708 .B " mdadm --create --help"
1710 Provide help about the Create mode.
1712 .B " mdadm --config --help"
1714 Provide help about the format of the config file.
1718 Provide general help.
1729 lists all active md devices with information about them.
1731 uses this to find arrays when
1733 is given in Misc mode, and to monitor array reconstruction
1739 The config file lists which devices may be scanned to see if
1740 they contain MD super block, and gives identifying information
1741 (e.g. UUID) about known MD arrays. See
1747 While entries in the /dev directory can have any format you like,
1749 has an understanding of 'standard' formats which it uses to guide its
1750 behaviour when creating device files via the
1754 The standard names for non-partitioned arrays (the only sort of md
1755 array available in 2.4 and earlier) either of
1761 where NN is a number.
1762 The standard names for partitionable arrays (as available from 2.6
1769 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
1773 was previously known as
1777 is completely separate from the
1779 package, and does not use the
1781 configuration file at all.
1784 For information on the various levels of
1788 .UR http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1789 http://ostenfeld.dk/~jakob/Software-RAID.HOWTO/
1792 '''for new releases of the RAID driver check out:
1795 '''.UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1796 '''ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
1801 '''.UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1802 '''http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
1805 The latest version of
1807 should always be available from
1809 .UR http://www.kernel.org/pub/linux/utils/raid/mdadm/
1810 http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob