[Users] RE: slow fsync rate

[Kir Kolyshkin]

On 08/26/2010 12:59 PM, Martin Maurer wrote:
> Hi Kir,
>
> Yes, the performance number shows that it does not use the cache so if anyone want to run high load like a database on such a system the performance loss will be significant and the system will be more or less unusable (compared to current stable). I got this behavior ONLY with 2.6.32 OpenVZ kernels. E.g. also the standard Debian Squeeze Kernel (also 2.6.32) give the expected performance, the OpenVZ enabled kernel from Squeeze doesn´t. (see also http://lists.debian.org/debian-kernel/2010/08/msg00217.html).
>
> We tested on several hardware and distributions, e.g. with single drives, hardware raid controllers with BBU - e.g. the Intel Modular Server but also on single drives on ICH7/8/9. The logs always shows that the disk has read and write cache enabled, but the values are just bad.
>
> Can you reproduce the issue (just run the sysbench command: "sysbench --test=fileio --file-num=1 --file-total-size=50G --file-fsync-all=on --file-test-mode=seqrewr --max-time=100 --file-block-size=4096 --max-requests=0 run")?
>    

OK, at this point I guess it makes sense to file a bug, please do that.

As a workaround, try to change block device scheduler from
cfq to a different one (note though that ioprio will stop working).