[zfs-discuss] Improving snapshot write performance

Ian Collins
2012-04-12T04:24:30Z

On 04/12/12 09:51 AM, Peter Jeremy wrote:
> On 2012-Apr-11 18:34:42 +1000, Ian Collins<ian at ianshome.com>
wrote:
>> I use an application with a fairly large receive data buffer (256MB) to
>> replicate data between sites.
>>
>> I have noticed the buffer becoming completely full when receiving
>> snapshots for some filesystems, even over a slow (~2MB/sec) WAN
>> connection.  I assume this is due to the changes being widely
scattered.
> As Richard pointed out, the write side should be mostly contiguous.
>
>> Is there any way to improve this situation?
> Is the target pool nearly full (so ZFS is spending lots of time searching
> for free space)?
>
> Do you have dedupe enabled on the target pool?  This would force ZFS to
> search the DDT to write blocks - this will be expensive, especially if
> you don''t have enough RAM.
>
> Do yoy have a high compression level (gzip or gzip-N) on the target
> filesystems, without enough CPU horsepower?
>
> Do you have a dying (or dead) disk in the target pool?
>

No to all of the above!

--
Ian.