From: NeilBrown <neilb@suse.de>
To: Sebastian Riemer <sebastian.riemer@profitbricks.com>
Cc: linux-raid@vger.kernel.org
Subject: Re: Reason for md raid 01 blksize limited to 4 KiB?
Date: Tue, 22 May 2012 09:28:17 +1000 [thread overview]
Message-ID: <20120522092817.1b5946b8@notabene.brown> (raw)
In-Reply-To: <4FBA0047.5050208@profitbricks.com>
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On Mon, 21 May 2012 10:43:51 +0200 Sebastian Riemer
<sebastian.riemer@profitbricks.com> wrote:
> Hi list,
>
> I'm wondering why stacking raid1 above raid0 limits the block sizes in
> the blkio queue to 4 KiB both read and write.
>
> The max_sectors_kb is at 512. So it's not a matter of limits.
>
> Could someone explain, please? Or could someone pinpoint me to the
> related location in the source code?
>
> We've thought of using this for replication via InfiniBand/SRP. 4 KiB
> chunks are completely inefficient with SRP. We wanted to do this with
> DRBD first, but this is also extremely inefficient, because of chunk
> sizes in the blkio queue.
>
> I can reproduce the small 4 KiB chunks also in a file copy benchmark
> with raid 01 on ram disks.
This should be fixed in linux 3.4 with commit 6b740b8d79252f13bcb7e5d3c1d
NeilBrown
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next prev parent reply other threads:[~2012-05-21 23:28 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-21 8:43 Reason for md raid 01 blksize limited to 4 KiB? Sebastian Riemer
2012-05-21 23:14 ` Stan Hoeppner
2012-05-21 23:28 ` NeilBrown [this message]
2012-05-25 12:35 ` Sebastian Riemer
2012-05-28 4:05 ` NeilBrown
2012-05-29 9:30 ` Sebastian Riemer
2012-05-29 10:25 ` NeilBrown
2012-05-30 13:03 ` Sebastian Riemer
2012-05-31 5:42 ` NeilBrown
2012-05-31 6:18 ` Yuanhan Liu
2012-05-31 10:26 ` Sebastian Riemer
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