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Re: [dm-devel] [PATCH] dm-thin: Add data block size limits to the Documentation



On 07/24/2013 11:32 AM, Heinz Mauelshagen wrote:
On 07/23/2013 04:03 PM, Carlos Maiolino wrote:
$data_block_size can't be any arbitrary number, i.e. its value should be between
64K and 1G. Also, it should be a multiple of 64K.

The limits 64K and 1G are correct and enforced by the pool constructor in the target.

Blocksize is _not_ a multiple of 64K; it has to be power of 2.

Thus 64K,128K,256K,512K and 1G are valid block sizes for the pool with the current pool constructor limits enforced.

Correction self: 64K increments are upstream -> your patch is correct.


-- lvmguy

Add this information to the dm-thin documentation in order to let users know
which values they must use.

Signed-off-by: Carlos Maiolino <cmaiolino redhat com>
---
  Documentation/device-mapper/thin-provisioning.txt | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/device-mapper/thin-provisioning.txt b/Documentation/device-mapper/thin-provisioning.txt
index 30b8b83..ff1629b 100644
--- a/Documentation/device-mapper/thin-provisioning.txt
+++ b/Documentation/device-mapper/thin-provisioning.txt
@@ -104,8 +104,8 @@ 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.
+$data_block_size must be between 128 (64KB) and 2097152 (1GB) and be a multiple
+of 128 (64KB), and the same for the lifetime of the metadata device.
    $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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