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dm thin: add data block size limits to Documentation 

Inform users that the data block size can't be any arbitrary number,
i.e. its value must be between 64KB and 1GB.  Also, it should be a
multiple of 64KB.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
This commit is contained in:
Carlos Maiolino 2013-07-23 11:03:16 -03:00 committed by Mike Snitzer
parent 0547304463
commit a561ddbec1
1 changed files with 8 additions and 7 deletions
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15
Documentation/device-mapper/thin-provisioning.txt
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@ -99,13 +99,14 @@ Using an existing pool device
$data_block_size $low_water_mark"
$data_block_size gives the smallest unit of disk space that can be
allocated at a time expressed in units of 512-byte sectors. People
primarily interested in thin provisioning may want to use a value such
as 1024 (512KB). People doing lots of snapshotting may want a smaller value
such as 128 (64KB). If you are not zeroing newly-allocated data,
a larger $data_block_size in the region of 256000 (128MB) is suggested.
$data_block_size must be the same for the lifetime of the
metadata device.
allocated at a time expressed in units of 512-byte sectors.
$data_block_size must be between 128 (64KB) and 2097152 (1GB) and a
multiple of 128 (64KB). $data_block_size cannot be changed after the
thin-pool is created. People primarily interested in thin provisioning
may want to use a value such as 1024 (512KB). People doing lots of
snapshotting may want a smaller value such as 128 (64KB). If you are
not zeroing newly-allocated data, a larger $data_block_size in the
region of 256000 (128MB) is suggested.
$low_water_mark is expressed in blocks of size $data_block_size. If
free space on the data device drops below this level then a dm event