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Documentation/md.txt update

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Update md.txt to reflect recent changes in a number of sysfs
attributes.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2009-03-31 15:18:37 +11:00
parent ec32a2bd35
commit 1137354234
1 changed files with 30 additions and 7 deletions
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37
Documentation/md.txt
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@ -164,15 +164,19 @@ All md devices contain:
raid_disks raid_disks
a text file with a simple number indicating the number of devices 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 in a fully functional array. If this is not yet known, the file
will be empty. If an array is being resized (not currently will be empty. If an array is being resized this will contain
possible) this will contain the larger of the old and new sizes. the new number of devices.
Some raid level (RAID1) allow this value to be set while the Some raid levels allow this value to be set while the array is
array is active. This will reconfigure the array. Otherwise active. This will reconfigure the array. Otherwise it can only
it can only be set while assembling an array. 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 chunk_size
This is the size if 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 (1,4,5,6,10). The address space raid levels that involve striping (0,4,5,6,10). The address space
of the array is conceptually divided into chunks and consecutive of the array is conceptually divided into chunks and consecutive
chunks are striped onto neighbouring devices. chunks are striped onto neighbouring devices.
The size should be at least PAGE_SIZE (4k) and should be a power The size should be at least PAGE_SIZE (4k) and should be a power
@ -183,6 +187,20 @@ All md devices contain:
simply a number that is interpretted differently by different simply a number that is interpretted differently by different
levels. It can be written while assembling an array. 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 reshape_position
This is either "none" or a sector number within the devices of 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 the array where "reshape" is up to. If this is set, the three
@ -207,6 +225,11 @@ All md devices contain:
about the array. It can be 0.90 (traditional format), 1.0, 1.1, 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. 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 resync_start
The point at which resync should start. If no resync is needed, The point at which resync should start. If no resync is needed,