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

[Heinz Mauelshagen]

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 at 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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