Re: Terrible performance of sequential O_DIRECT 4k writes in SAN environment. ~3 times slower then Solars 10 with the same HBA/Storage.

Sergey Meirovich
2014-01-08T14:43:07Z

Hi Christoph,

On 8 January 2014 16:03, Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Jan 07, 2014 at 08:37:23PM +0200, Sergey Meirovich wrote:
>> Actually my initial report (14.67Mb/sec 3755.41 Requests/sec) was about ext4
>> However I have tried XFS as well. It was a bit slower than ext4 on all
>> occasions.
>
> I wasn't trying to say XFS fixes your problem, but that we could
> implement appending AIO writes in XFS fairly easily.
>
> To verify Jan's theory, can you try to preallocate the file to the full
> size and then run the benchmark by doing a:
>
> # fallocate -l <size> <filename>
>
> and then run it? If that's indeed the issue I'd be happy to implement
> the "real aio" append support for you as well.
>

After fallocate:
[root@illin01 ext4]# du -k test_file.* | awk '{print $1}' |sort |uniq
81920
[root@illin01 ext4]# fallocate -l 81920k test_file.*

Results are almost the same:
14.68Mb/sec 3758.02 Requests/sec