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

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Date:	Wed, 8 Jan 2014 16:43:07 +0200
From:	Sergey Meirovich <rathamahata@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, linux-scsi <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Gluk <git.user@...il.com>
Subject: Re: Terrible performance of sequential O_DIRECT 4k writes in SAN
 environment. ~3 times slower then Solars 10 with the same HBA/Storage.

Hi Christoph,

On 8 January 2014 16:03, Christoph Hellwig <hch@...radead.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@...in01 ext4]# du -k test_file.* | awk '{print $1}' |sort |uniq
81920
[root@...in01 ext4]# fallocate -l 81920k test_file.*

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