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-rw-r--r--Documentation/device-mapper/thin-provisioning.txt15
1 files changed, 8 insertions, 7 deletions
diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index 30b8b83bd333..50c44cf79b0e 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -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
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