Tools that manage md devices can be found at
- http://www.<country>.kernel.org/pub/linux/utils/raid/....
+ http://www.kernel.org/pub/linux/utils/raid/
Boot time assembly of RAID arrays
Then uninitialized devices can be added with ADD_NEW_DISK. The
structure passed to ADD_NEW_DISK must specify the state of the device
-and it's role in the array.
+and its role in the array.
Once started with RUN_ARRAY, uninitialized spares can be added with
HOT_ADD_DISK.
raid_disks
a text file with a simple number indicating the number of devices
in a fully functional array. If this is not yet known, the file
- will be empty. If an array is being resized (not currently
- possible) this will contain the larger of the old and new sizes.
- Some raid level (RAID1) allow this value to be set while the
- array is active. This will reconfigure the array. Otherwise
- it can only be set while assembling an array.
+ will be empty. If an array is being resized this will contain
+ the new number of devices.
+ Some raid levels allow this value to be set while the array is
+ active. This will reconfigure the array. Otherwise it can only
+ be set while assembling an array.
+ A change to this attribute will not be permitted if it would
+ reduce the size of the array. To reduce the number of drives
+ in an e.g. raid5, the array size must first be reduced by
+ setting the 'array_size' attribute.
chunk_size
- This is the size if bytes for 'chunks' and is only relevant to
- raid levels that involve striping (1,4,5,6,10). The address space
+ This is the size in bytes for 'chunks' and is only relevant to
+ raid levels that involve striping (0,4,5,6,10). The address space
of the array is conceptually divided into chunks and consecutive
chunks are striped onto neighbouring devices.
The size should be at least PAGE_SIZE (4k) and should be a power
simply a number that is interpretted differently by different
levels. It can be written while assembling an array.
+ array_size
+ This can be used to artificially constrain the available space in
+ the array to be less than is actually available on the combined
+ devices. Writing a number (in Kilobytes) which is less than
+ the available size will set the size. Any reconfiguration of the
+ array (e.g. adding devices) will not cause the size to change.
+ Writing the word 'default' will cause the effective size of the
+ array to be whatever size is actually available based on
+ 'level', 'chunk_size' and 'component_size'.
+
+ This can be used to reduce the size of the array before reducing
+ the number of devices in a raid4/5/6, or to support external
+ metadata formats which mandate such clipping.
+
reshape_position
This is either "none" or a sector number within the devices of
the array where "reshape" is up to. If this is set, the three
about the array. It can be 0.90 (traditional format), 1.0, 1.1,
1.2 (newer format in varying locations) or "none" indicating that
the kernel isn't managing metadata at all.
+ Alternately it can be "external:" followed by a string which
+ is set by user-space. This indicates that metadata is managed
+ by a user-space program. Any device failure or other event that
+ requires a metadata update will cause array activity to be
+ suspended until the event is acknowledged.
resync_start
The point at which resync should start. If no resync is needed,
- this will be a very large number. At array creation it will
- default to 0, though starting the array as 'clean' will
- set it much larger.
+ this will be a very large number (or 'none' since 2.6.30-rc1). At
+ array creation it will default to 0, though starting the array as
+ 'clean' will set it much larger.
new_dev
This file can be written but not read. The value written should
active-idle
like active, but no writes have been seen for a while (safe_mode_delay).
+ bitmap/location
+ This indicates where the write-intent bitmap for the array is
+ stored.
+ It can be one of "none", "file" or "[+-]N".
+ "file" may later be extended to "file:/file/name"
+ "[+-]N" means that many sectors from the start of the metadata.
+ This is replicated on all devices. For arrays with externally
+ managed metadata, the offset is from the beginning of the
+ device.
+ bitmap/chunksize
+ The size, in bytes, of the chunk which will be represented by a
+ single bit. For RAID456, it is a portion of an individual
+ device. For RAID10, it is a portion of the array. For RAID1, it
+ is both (they come to the same thing).
+ bitmap/time_base
+ The time, in seconds, between looking for bits in the bitmap to
+ be cleared. In the current implementation, a bit will be cleared
+ between 2 and 3 times "time_base" after all the covered blocks
+ are known to be in-sync.
+ bitmap/backlog
+ When write-mostly devices are active in a RAID1, write requests
+ to those devices proceed in the background - the filesystem (or
+ other user of the device) does not have to wait for them.
+ 'backlog' sets a limit on the number of concurrent background
+ writes. If there are more than this, new writes will by
+ synchronous.
+ bitmap/metadata
+ This can be either 'internal' or 'external'.
+ 'internal' is the default and means the metadata for the bitmap
+ is stored in the first 256 bytes of the allocated space and is
+ managed by the md module.
+ 'external' means that bitmap metadata is managed externally to
+ the kernel (i.e. by some userspace program)
+ bitmap/can_clear
+ This is either 'true' or 'false'. If 'true', then bits in the
+ bitmap will be cleared when the corresponding blocks are thought
+ to be in-sync. If 'false', bits will never be cleared.
+ This is automatically set to 'false' if a write happens on a
+ degraded array, or if the array becomes degraded during a write.
+ When metadata is managed externally, it should be set to true
+ once the array becomes non-degraded, and this fact has been
+ recorded in the metadata.
+
+
+
As component devices are added to an md array, they appear in the 'md'
directory as new directories named
A file recording the current state of the device in the array
which can be a comma separated list of
faulty - device has been kicked from active use due to
- a detected fault
+ a detected fault or it has unacknowledged bad
+ blocks
in_sync - device is a fully in-sync member of the array
writemostly - device will only be subject to read
requests if there are no other options.
This applies only to raid1 arrays.
+ blocked - device has failed, and the failure hasn't been
+ acknowledged yet by the metadata handler.
+ Writes that would write to this device if
+ it were not faulty are blocked.
spare - device is working, but not a full member.
This includes spares that are in the process
of being recovered to
+ write_error - device has ever seen a write error.
This list may grow in future.
This can be written to.
Writing "faulty" simulates a failure on the device.
Writing "remove" removes the device from the array.
Writing "writemostly" sets the writemostly flag.
Writing "-writemostly" clears the writemostly flag.
+ Writing "blocked" sets the "blocked" flag.
+ Writing "-blocked" clears the "blocked" flags and allows writes
+ to complete and possibly simulates an error.
+ Writing "in_sync" sets the in_sync flag.
+ Writing "write_error" sets writeerrorseen flag.
+ Writing "-write_error" clears writeerrorseen flag.
+
+ This file responds to select/poll. Any change to 'faulty'
+ or 'blocked' causes an event.
errors
An approximate count of read errors that have been detected on
for storage of data. This will normally be the same as the
component_size. This can be written while assembling an
array. If a value less than the current component_size is
- written, component_size will be reduced to this value.
+ written, it will be rejected.
+
+ recovery_start
+ When the device is not 'in_sync', this records the number of
+ sectors from the start of the device which are known to be
+ correct. This is normally zero, but during a recovery
+ operation is will steadily increase, and if the recovery is
+ interrupted, restoring this value can cause recovery to
+ avoid repeating the earlier blocks. With v1.x metadata, this
+ value is saved and restored automatically.
+
+ This can be set whenever the device is not an active member of
+ the array, either before the array is activated, or before
+ the 'slot' is set.
+
+ Setting this to 'none' is equivalent to setting 'in_sync'.
+ Setting to any other value also clears the 'in_sync' flag.
+
+ bad_blocks
+ This gives the list of all known bad blocks in the form of
+ start address and length (in sectors respectively). If output
+ is too big to fit in a page, it will be truncated. Writing
+ "sector length" to this file adds new acknowledged (i.e.
+ recorded to disk safely) bad blocks.
+
+ unacknowledged_bad_blocks
+ This gives the list of known-but-not-yet-saved-to-disk bad
+ blocks in the same form of 'bad_blocks'. If output is too big
+ to fit in a page, it will be truncated. Writing to this file
+ adds bad blocks without acknowledging them. This is largely
+ for testing.
+
An active md device will also contain and entry for each active device
achieved. In that case, the transition to "recover" isn't
notified, but the transition away is.
+ degraded
+ This contains a count of the number of devices by which the
+ arrays is degraded. So an optimal array with show '0'. A
+ single failed/missing drive will show '1', etc.
+ This file responds to select/poll, any increase or decrease
+ in the count of missing devices will trigger an event.
+
mismatch_count
When performing 'check' and 'repair', and possibly when
performing 'resync', md will count the number of errors that are
within the array where IO will be blocked. This is currently
only supported for raid4/5/6.
+ sync_min
+ sync_max
+ The two values, given as numbers of sectors, indicate a range
+ within the array where 'check'/'repair' will operate. Must be
+ a multiple of chunk_size. When it reaches "sync_max" it will
+ pause, rather than complete.
+ You can use 'select' or 'poll' on "sync_completed" to wait for
+ that number to reach sync_max. Then you can either increase
+ "sync_max", or can write 'idle' to "sync_action".
+
Each active md device may also have attributes specific to the
personality module that manages it.
projects / linux-flexiantxendom0.git / blobdiff