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Date: Tue, 10 Apr 2012 07:47:36 +1000
From: Dave Chinner <david@fromorbit.com>
Subject: Re: XFS: Abysmal write performance because of excessive seeking
	(allocation groups to blame?)
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To: Emmanuel Florac <eflorac@intellique.com>
Cc: Stefan Ring <stefanrin@gmail.com>, stan@hardwarefreak.com, Linux fs XFS <xfs@oss.sgi.com>

On Mon, Apr 09, 2012 at 01:39:13PM +0200, Emmanuel Florac wrote:
> Le Mon, 9 Apr 2012 10:19:43 +1000 vous =E9criviez:
> =

> > A decent RAID controller with a BBWC and a single LUN benefits from
> > parallelism just as much as a large disk arrays do because the BBWC
> > minimises the write IO latency and the controller to do a better job
> > of scheduling its IO.
> =

> BTW recently I've found that for storage servers, noop io scheduler
> often is the best choice, I suppose precisely because it doesn't try to
> outsmart the RAID controller logic...

We've been recommending the use of the no-op (or worst case,
deadline) scheduler for XFS on hardware RAID for quite a few years.
I only test against the no-op scheduler, because I got sick of
having to track down regressions caused by "smart" CFQ heuristics....

Cheers,

Dave.
-- =

Dave Chinner
david@fromorbit.com

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