Documentation/admin-guide/md.rst

22 or, to assemble a partitionable array::
44 level of the RAID array
92 If a raid5 or raid6 array is both dirty and degraded, it could have
98 For this reason, md will normally refuse to start such an array.  This
99 requires the sysadmin to take action to explicitly start the array
104 This option is not really available if the array has the root
106 array, md supports a module parameter ``start_dirty_degraded`` which,
131 An array is ``created`` by writing appropriate superblocks to all
138 An array should be created by a user-space tool.  This will write
139 superblocks to all devices.  It will usually mark the array as
144 When an array is assembled, it is first initialized with the
155 The array is started with the RUN_ARRAY ioctl.
162 array using HOT_REMOVE_DISK.
168 An array can be ``created`` by describing the array (level, chunksize
174 and its role in the array.
196      If no raid level has been set yet (array is still being
203      in a fully functional array.  If this is not yet known, the file
204      will be empty.  If an array is being resized this will contain
206      Some raid levels allow this value to be set while the array is
207      active.  This will reconfigure the array.   Otherwise it can only
208      be set while assembling an array.
210      reduce the size of the array.  To reduce the number of drives
211      in an e.g. raid5, the array size must first be reduced by
217      of the array is conceptually divided into chunks and consecutive
220      of 2.  This can only be set while assembling an array
223      The ``layout`` for the array for the particular level.  This is
225      levels.  It can be written while assembling an array.
229      the array to be less than is actually available on the combined
232      array (e.g. adding devices) will not cause the size to change.
234      array to be whatever size is actually available based on
237      This can be used to reduce the size of the array before reducing
242      Configure the array's logical block size in bytes. This attribute
244      array. The final array LBS uses the maximum between this
253      the array where ``reshape`` is up to.  If this is set, the three
267      part or the geometry of the array.  It is measured in sectors
269      the array if the personality supports it (raid1, raid5, raid6),
274      about the array.  It can be 0.90 (traditional format), 1.0, 1.1,
280      requires a metadata update will cause array activity to be
286      array creation it will default to 0, though starting the array as
292      This will cause that device to be attached to the array, if it is
297      When an md array has seen no write requests for a certain period
299      request arrives, the array is marked as ``dirty`` before the write
307      state of the array.  In many cases, the state can be set by
322          May have some settings, but array is not active
325          When written, doesn't tear down array, but just stops it
328          All IO requests will block. The array can be reconfigured.
330          Writing this, if accepted, will block until array is quiescent
343          When written to inactive array, starts without resync
349          If written to an active array that has pending writes, then fails.
352          When written to inactive array, starts with resync
361      This indicates how the array maintains consistency in case of unexpected
365        Array has no redundancy information, e.g. raid0, linear.
369        array is started after unclean shutdown.
386      This indicates the UUID of the array in the following format:
391      bitmap for this array. The currently active bitmap will be enclosed
393      control of this array to that new bitmap. Note that writing a new
394      bitmap for created array is forbidden.
409      This indicates where the write-intent bitmap for the array is
423      device. For RAID10, it is a portion of the array.  For RAID1, it
457      degraded array, or if the array becomes degraded during a write.
459      once the array becomes non-degraded, and this fact has been
480 As component devices are added to an md array, they appear in the ``md``
498 	A file recording the current state of the device in the array
507 			device is a fully in-sync member of the array
547 	Writing ``remove`` removes the device from the array.
571 	starting the array.  It sets or clears the flag.
580 	the array (either because they were corrected or because they
581 	happened while the array was read-only).  When using version-1
582 	metadata, this value persists across restarts of the array.
584 	This value can be written while assembling an array thus
589         This gives the role that the device has in the array.  It will
590 	either be ``none`` if the device is not active in the array
592 	``raid_disks`` number for the array indicating which position
594 	array.  A device for which this is set is assumed to be working.
598         start) where data from the array will be stored.  Any part of
606         array.  If a value less than the current component_size is
619 	the array, either before the array is activated, or before
645 in the array.  These are named::
649 where ``NN`` is the position in the array, starting from 0.
650 So for a 3 drive array there will be rd0, rd1, rd2.
711       arrays is degraded.  So an optimal array will show ``0``.  A
727       If the array has a write-intent bitmap, then writing to this
738      however they only apply to the particular array.
765      within the array where IO will be blocked.  This is currently
770      within the array where ``check``/``repair`` will operate. Must be