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Documentation/md.txt: Convert to ReST markup

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- add a title for the document;
- convert some parameters to tables;
- use quote blocks where needed;
- use monotonic fonts for parameters;
- adjust whitespaces and blank lines;
- add it to the user's book.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab 2016-09-23 13:22:41 -03:00
parent 9a11e15381
commit aeb04e52f1
1 changed files with 317 additions and 203 deletions
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Documentation/md.txt
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@ -1,42 +1,77 @@
Tools that manage md devices can be found at
http://www.kernel.org/pub/linux/utils/raid/
RAID arrays
===========
Boot time assembly of RAID arrays
---------------------------------
Tools that manage md devices can be found at
http://www.kernel.org/pub/linux/utils/raid/
You can boot with your md device with the following kernel command
lines:
for old raid arrays without persistent superblocks:
for old raid arrays without persistent superblocks::
md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn
for raid arrays with persistent superblocks
for raid arrays with persistent superblocks::
md=<md device no.>,dev0,dev1,...,devn
or, to assemble a partitionable array:
or, to assemble a partitionable array::
md=d<md device no.>,dev0,dev1,...,devn
md device no. = the number of the md device ...
0 means md0,
1 md1,
2 md2,
3 md3,
4 md4
raid level = -1 linear mode
0 striped mode
other modes are only supported with persistent super blocks
``md device no.``
+++++++++++++++++
chunk size factor = (raid-0 and raid-1 only)
Set the chunk size as 4k << n.
fault level = totally ignored
dev0-devn: e.g. /dev/hda1,/dev/hdc1,/dev/sda1,/dev/sdb1
A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this:
The number of the md device
e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro
================= =========
``md device no.`` device
================= =========
0 md0
1 md1
2 md2
3 md3
4 md4
================= =========
``raid level``
++++++++++++++
level of the RAID array
=============== =============
``raid level`` level
=============== =============
-1 linear mode
0 striped mode
=============== =============
other modes are only supported with persistent super blocks
``chunk size factor``
+++++++++++++++++++++
(raid-0 and raid-1 only)
Set the chunk size as 4k << n.
``fault level``
+++++++++++++++
Totally ignored
``dev0`` to ``devn``
++++++++++++++++++++
e.g. ``/dev/hda1``, ``/dev/hdc1``, ``/dev/sda1``, ``/dev/sdb1``
A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this::
e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro
Boot time autodetection of RAID arrays
@ -45,10 +80,10 @@ Boot time autodetection of RAID arrays
When md is compiled into the kernel (not as module), partitions of
type 0xfd are scanned and automatically assembled into RAID arrays.
This autodetection may be suppressed with the kernel parameter
"raid=noautodetect". As of kernel 2.6.9, only drives with a type 0
``raid=noautodetect``. As of kernel 2.6.9, only drives with a type 0
superblock can be autodetected and run at boot time.
The kernel parameter "raid=partitionable" (or "raid=part") means
The kernel parameter ``raid=partitionable`` (or ``raid=part``) means
that all auto-detected arrays are assembled as partitionable.
Boot time assembly of degraded/dirty arrays
@ -56,22 +91,23 @@ Boot time assembly of degraded/dirty arrays
If a raid5 or raid6 array is both dirty and degraded, it could have
undetectable data corruption. This is because the fact that it is
'dirty' means that the parity cannot be trusted, and the fact that it
``dirty`` means that the parity cannot be trusted, and the fact that it
is degraded means that some datablocks are missing and cannot reliably
be reconstructed (due to no parity).
For this reason, md will normally refuse to start such an array. This
requires the sysadmin to take action to explicitly start the array
despite 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
filesystem on it. In order to support this booting from such an
array, md supports a module parameter "start_dirty_degraded" which,
array, md supports a module parameter ``start_dirty_degraded`` which,
when set to 1, bypassed the checks and will allows dirty degraded
arrays to be started.
So, to boot with a root filesystem of a dirty degraded raid[56], use
So, to boot with a root filesystem of a dirty degraded raid 5 or 6, use::
md-mod.start_dirty_degraded=1
@ -80,30 +116,30 @@ Superblock formats
------------------
The md driver can support a variety of different superblock formats.
Currently, it supports superblock formats "0.90.0" and the "md-1" format
Currently, it supports superblock formats ``0.90.0`` and the ``md-1`` format
introduced in the 2.5 development series.
The kernel will autodetect which format superblock is being used.
Superblock format '0' is treated differently to others for legacy
Superblock format ``0`` is treated differently to others for legacy
reasons - it is the original superblock format.
General Rules - apply for all superblock formats
------------------------------------------------
An array is 'created' by writing appropriate superblocks to all
An array is ``created`` by writing appropriate superblocks to all
devices.
It is 'assembled' by associating each of these devices with an
It is ``assembled`` by associating each of these devices with an
particular md virtual device. Once it is completely assembled, it can
be accessed.
An array should be created by a user-space tool. This will write
superblocks to all devices. It will usually mark the array as
'unclean', or with some devices missing so that the kernel md driver
can create appropriate redundancy (copying in raid1, parity
calculation in raid4/5).
``unclean``, or with some devices missing so that the kernel md driver
can create appropriate redundancy (copying in raid 1, parity
calculation in raid 4/5).
When an array is assembled, it is first initialized with the
SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor
@ -126,13 +162,12 @@ Devices that have failed or are not yet active can be detached from an
array using HOT_REMOVE_DISK.
Specific Rules that apply to format-0 super block arrays, and
arrays with no superblock (non-persistent).
-------------------------------------------------------------
Specific Rules that apply to format-0 super block arrays, and arrays with no superblock (non-persistent)
--------------------------------------------------------------------------------------------------------
An array can be 'created' by describing the array (level, chunksize
etc) in a SET_ARRAY_INFO ioctl. This must have major_version==0 and
raid_disks != 0.
An array can be ``created`` by describing the array (level, chunksize
etc) in a SET_ARRAY_INFO ioctl. This must have ``major_version==0`` and
``raid_disks != 0``.
Then uninitialized devices can be added with ADD_NEW_DISK. The
structure passed to ADD_NEW_DISK must specify the state of the device
@ -142,24 +177,26 @@ Once started with RUN_ARRAY, uninitialized spares can be added with
HOT_ADD_DISK.
MD devices in sysfs
-------------------
md devices appear in sysfs (/sys) as regular block devices,
e.g.
md devices appear in sysfs (``/sys``) as regular block devices,
e.g.::
/sys/block/md0
Each 'md' device will contain a subdirectory called 'md' which
Each ``md`` device will contain a subdirectory called ``md`` which
contains further md-specific information about the device.
All md devices contain:
level
a text file indicating the 'raid level'. e.g. raid0, raid1,
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), 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.
such as ``0``, ``5``, etc.
raid_disks
a text file with a simple number indicating the number of devices
@ -172,10 +209,10 @@ All md devices contain:
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.
setting the ``array_size`` attribute.
chunk_size
This is the size in bytes for 'chunks' and is only relevant to
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.
@ -183,7 +220,7 @@ All md devices contain:
of 2. This can only be set while assembling an array
layout
The "layout" for the array for the particular level. This is
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.
@ -193,22 +230,24 @@ All md devices contain:
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
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'.
``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
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
values differ, reading the attribute returns::
new (old)
and writing will effect the 'new' value, leaving the 'old'
and writing will effect the ``new`` value, leaving the ``old``
unchanged.
component_size
@ -223,9 +262,9 @@ All md devices contain:
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
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
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
@ -233,9 +272,9 @@ All md devices contain:
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
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.
``clean`` will set it much larger.
new_dev
This file can be written but not read. The value written should
@ -246,10 +285,10 @@ All md devices contain:
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
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.
@ -260,38 +299,50 @@ All md devices contain:
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.
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
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.
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 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.
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).
@ -299,57 +350,71 @@ All md devices contain:
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.
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
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
``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)
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
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
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
As component devices are added to an md array, they appear in the ``md``
directory as new directories named::
dev-XXX
where XXX is a name that the kernel knows for the device, e.g. hdb1.
where ``XXX`` is a name that the kernel knows for the device, e.g. hdb1.
Each directory contains:
block
a symlink to the block device in /sys/block, e.g.
a symlink to the block device in /sys/block, e.g.::
/sys/block/md0/md/dev-hdb1/block -> ../../../../block/hdb/hdb1
super
@ -358,51 +423,83 @@ Each directory contains:
state
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, 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.
want_replacement - device is (mostly) working but probably
should be replaced, either due to errors or
due to user request.
replacement - device is a replacement for another active
device with same raid_disk.
which can be a comma separated list of:
faulty
device has been kicked from active use due to
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.
want_replacement
device is (mostly) working but probably
should be replaced, either due to errors or
due to user request.
replacement
device is a replacement for another active
device with same raid_disk.
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.
Writing "want_replacement" is allowed at any time except to a
replacement device or a spare. It sets the flag.
Writing "-want_replacement" is allowed at any time. It clears
the flag.
Writing "replacement" or "-replacement" is only allowed before
starting the array. It sets or clears the flag.
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.
Writing ``want_replacement`` is allowed at any time except to a
replacement device or a spare. It sets the flag.
Writing ``-want_replacement`` is allowed at any time. It clears
the flag.
Writing ``replacement`` or ``-replacement`` is only allowed before
starting the array. It sets or clears the flag.
This file responds to select/poll. Any change to 'faulty'
or 'blocked' causes an event.
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
@ -417,9 +514,9 @@ Each directory contains:
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
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
``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.
@ -437,7 +534,7 @@ Each directory contains:
written, it will be rejected.
recovery_start
When the device is not 'in_sync', this records the number of
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 it will steadily increase, and if the recovery is
@ -447,21 +544,21 @@ Each directory contains:
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.
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.
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.
``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
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.
@ -469,16 +566,18 @@ Each directory contains:
An active md device will also contain an entry for each active device
in the array. These are named
in the array. These are named::
rdNN
where 'NN' is the position 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,
These are symbolic links to the appropriate ``dev-XXX`` entry.
Thus, for example::
cat /sys/block/md*/md/rd*/state
will show 'in_sync' on every line.
will show ``in_sync`` on every line.
@ -488,50 +587,62 @@ also have
sync_action
a text file that can be used to monitor and control the rebuild
process. It contains one word which can be one of:
resync - redundancy is being recalculated after unclean
shutdown or creation
recover - a hot spare is being built to replace a
failed/missing device
idle - nothing is happening
check - A full check of redundancy was requested and is
happening. This reads all blocks and checks
them. A repair may also happen for some raid
levels.
repair - A full check and repair is happening. This is
similar to 'resync', but was requested by the
user, and the write-intent bitmap is NOT used to
optimise the process.
resync
redundancy is being recalculated after unclean
shutdown or creation
recover
a hot spare is being built to replace a
failed/missing device
idle
nothing is happening
check
A full check of redundancy was requested and is
happening. This reads all blocks and checks
them. A repair may also happen for some raid
levels.
repair
A full check and repair is happening. This is
similar to ``resync``, but was requested by the
user, and the write-intent bitmap is NOT used to
optimise the process.
This file is writable, and each of the strings that could be
read are meaningful for writing.
'idle' will stop an active resync/recovery etc. There is no
guarantee that another resync/recovery may not be automatically
started again, though some event will be needed to trigger
this.
'resync' or 'recovery' can be used to restart the
corresponding operation if it was stopped with 'idle'.
'check' and 'repair' will start the appropriate process
providing the current state is 'idle'.
``idle`` will stop an active resync/recovery etc. There is no
guarantee that another resync/recovery may not be automatically
started again, though some event will be needed to trigger
this.
``resync`` or ``recovery`` can be used to restart the
corresponding operation if it was stopped with ``idle``.
``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
``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 will show '0'. A
single failed/missing drive will show '1', etc.
arrays is degraded. So an optimal array will 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
found. The count in 'mismatch_cnt' is the number of sectors
that were re-written, or (for 'check') would have been
When performing ``check`` and ``repair``, and possibly when
performing ``resync``, md will count the number of errors that are
found. The count in ``mismatch_cnt`` is the number of sectors
that were re-written, or (for ``check``) would have been
re-written. As most raid levels work in units of pages rather
than sectors, this may be larger than the number of actual errors
by a factor of the number of sectors in a page.
@ -542,27 +653,30 @@ also have
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.
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}
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, or if the word 'system'
If no value has been written to these, or 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
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
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,
A ``select`` on this attribute will return when resync completes,
when it reaches the current sync_max (below) and possibly at
other times.
@ -570,26 +684,24 @@ also have
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
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.
sync_min
sync_max
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
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
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".
``sync_max``, or can write ``idle`` to ``sync_action``.
The value of 'max' for "sync_max" effectively disables the limit.
The value of ``max`` for ``sync_max`` effectively disables the limit.
When a resync is active, the value can only ever be increased,
never decreased.
The value of '0' is the minimum for "sync_min".
The value of ``0`` is the minimum for ``sync_min``.
@ -598,13 +710,15 @@ personality module that manages it.
These are specific to the implementation of the module and could
change substantially if the implementation changes.
These currently include
These currently include:
stripe_cache_size (currently raid5 only)
number of entries in the stripe cache. This is writable, but
there are upper and lower limits (32768, 17). Default is 256.
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