For this reason, md will normally refuse to start such an array. This
requires the sysadmin to take action to explicitly start the array
-desipite possible corruption. This is normally done with
+despite possible corruption. This is normally done with
mdadm --assemble --force ....
This option is not really available if the array has the root
All md devices contain:
level
- a text file indicating the 'raid level'. This may be a standard
- numerical level prefixed by "RAID-" - e.g. "RAID-5", or some
- other name such as "linear" or "multipath".
+ a text file indicating the 'raid level'. e.g. raid0, raid1,
+ raid5, linear, multipath, faulty.
If no raid level has been set yet (array is still being
- assembled), this file will be empty.
+ assembled), the value will reflect whatever has been written
+ to it, which may be a name like the above, or may be a number
+ such as '0', '5', etc.
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.
+ 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 atleast PAGE_SIZE (4k) and should be a power
+ The size should be at least PAGE_SIZE (4k) and should be a power
of 2. This can only be set while assembling an array
+ layout
+ The "layout" for the array for the particular level. This is
+ 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
+ attributes mentioned above (raid_disks, chunk_size, layout) can
+ potentially have 2 values, an old and a new value. If these
+ values differ, reading the attribute returns
+ new (old)
+ and writing will effect the 'new' value, leaving the 'old'
+ unchanged.
+
component_size
For arrays with data redundancy (i.e. not raid0, linear, faulty,
multipath), all components must be the same size - or at least
the array if the personality supports it (raid1, raid5, raid6),
and if the component drives are large enough.
+ metadata_version
+ This indicates the format that is being used to record metadata
+ 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 (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
+ be a block device number as major:minor. e.g. 8:0
+ This will cause that device to be attached to the array, if it is
+ available. It will then appear at md/dev-XXX (depending on the
+ name of the device) and further configuration is then possible.
+
+ safe_mode_delay
+ When an md array has seen no write requests for a certain period
+ of time, it will be marked as 'clean'. When another write
+ request arrives, the array is marked as 'dirty' before the write
+ commences. This is known as 'safe_mode'.
+ The 'certain period' is controlled by this file which stores the
+ period as a number of seconds. The default is 200msec (0.200).
+ Writing a value of 0 disables safemode.
+
+ array_state
+ This file contains a single word which describes the current
+ state of the array. In many cases, the state can be set by
+ writing the word for the desired state, however some states
+ cannot be explicitly set, and some transitions are not allowed.
+
+ Select/poll works on this file. All changes except between
+ active_idle and active (which can be frequent and are not
+ very interesting) are notified. active->active_idle is
+ reported if the metadata is externally managed.
+
+ clear
+ No devices, no size, no level
+ Writing is equivalent to STOP_ARRAY ioctl
+ inactive
+ May have some settings, but array is not active
+ all IO results in error
+ When written, doesn't tear down array, but just stops it
+ suspended (not supported yet)
+ All IO requests will block. The array can be reconfigured.
+ Writing this, if accepted, will block until array is quiessent
+ readonly
+ no resync can happen. no superblocks get written.
+ write requests fail
+ read-auto
+ like readonly, but behaves like 'clean' on a write request.
+
+ clean - no pending writes, but otherwise active.
+ When written to inactive array, starts without resync
+ If a write request arrives then
+ if metadata is known, mark 'dirty' and switch to 'active'.
+ if not known, block and switch to write-pending
+ If written to an active array that has pending writes, then fails.
+ active
+ fully active: IO and resync can be happening.
+ When written to inactive array, starts with resync
+
+ write-pending
+ clean, but writes are blocked waiting for 'active' to be written.
+
+ 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
dev-XXX
faulty - device has been kicked from active use due to
a detected fault
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, metadata is "external",
+ and the failure hasn't been acknowledged yet.
+ 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 recoverred to
- This list make grow in future.
+ of being recovered to
+ 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" flag and allows writes
+ to complete.
+ Writing "in_sync" sets the in_sync 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
+ this device but have not caused the device to be evicted from
+ the array (either because they were corrected or because they
+ happened while the array was read-only). When using version-1
+ metadata, this value persists across restarts of the array.
+
+ This value can be written while assembling an array thus
+ providing an ongoing count for arrays with metadata managed by
+ userspace.
+
+ slot
+ This gives the role that the device has in the array. It will
+ either be 'none' if the device is not active in the array
+ (i.e. is a spare or has failed) or an integer less than the
+ 'raid_disks' number for the array indicating which position
+ it currently fills. This can only be set while assembling an
+ array. A device for which this is set is assumed to be working.
+
+ offset
+ This gives the location in the device (in sectors from the
+ start) where data from the array will be stored. Any part of
+ the device before this offset us not touched, unless it is
+ used for storing metadata (Formats 1.1 and 1.2).
+
+ size
+ The amount of the device, after the offset, that can be used
+ 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, 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.
+
An active md device will also contain and entry for each active device
rdNN
-where 'NN' is the possition in the array, starting from 0.
+where 'NN' is the position in the array, starting from 0.
So for a 3 drive array there will be rd0, rd1, rd2.
These are symbolic links to the appropriate 'dev-XXX' entry.
Thus, for example,
'check' and 'repair' will start the appropriate process
providing the current state is 'idle'.
+ This file responds to select/poll. Any important change in the value
+ triggers a poll event. Sometimes the value will briefly be
+ "recover" if a recovery seems to be needed, but cannot be
+ 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
than sectors, this my be larger than the number of actual errors
by a factor of the number of sectors in a page.
+ bitmap_set_bits
+ If the array has a write-intent bitmap, then writing to this
+ attribute can set bits in the bitmap, indicating that a resync
+ would need to check the corresponding blocks. Either individual
+ numbers or start-end pairs can be written. Multiple numbers
+ can be separated by a space.
+ Note that the numbers are 'bit' numbers, not 'block' numbers.
+ They should be scaled by the bitmap_chunksize.
+
+ sync_speed_min
+ sync_speed_max
+ This are similar to /proc/sys/dev/raid/speed_limit_{min,max}
+ however they only apply to the particular array.
+ If no value has been written to these, of if the word 'system'
+ is written, then the system-wide value is used. If a value,
+ in kibibytes-per-second is written, then it is used.
+ When the files are read, they show the currently active value
+ followed by "(local)" or "(system)" depending on whether it is
+ a locally set or system-wide value.
+
+ sync_completed
+ This shows the number of sectors that have been completed of
+ whatever the current sync_action is, followed by the number of
+ sectors in total that could need to be processed. The two
+ numbers are separated by a '/' thus effectively showing one
+ value, a fraction of the process that is complete.
+ A 'select' on this attribute will return when resync completes,
+ when it reaches the current sync_max (below) and possibly at
+ other times.
+
+ sync_max
+ This is a number of sectors at which point a resync/recovery
+ process will pause. When a resync is active, the value can
+ only ever be increased, never decreased. The value of 'max'
+ effectively disables the limit.
+
+
+ sync_speed
+ This shows the current actual speed, in K/sec, of the current
+ sync_action. It is averaged over the last 30 seconds.
+
+ suspend_lo
+ suspend_hi
+ The two values, given as numbers of sectors, indicate a range
+ within the array where IO will be blocked. This is currently
+ only supported for raid4/5/6.
+
+
Each active md device may also have attributes specific to the
personality module that manages it.
These are specific to the implementation of the module and could
there are upper and lower limits (32768, 16). Default is 128.
strip_cache_active (currently raid5 only)
number of active entries in the stripe cache
+ preread_bypass_threshold (currently raid5 only)
+ number of times a stripe requiring preread will be bypassed by
+ a stripe that does not require preread. For fairness defaults
+ to 1. Setting this to 0 disables bypass accounting and
+ requires preread stripes to wait until all full-width stripe-
+ writes are complete. Valid values are 0 to stripe_cache_size.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff