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Date: Thu, 5 Aug 2010 15:01:38 -0400
From: Chris Mason <chris.mason@oracle.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>, Valdis.Kletnieks@vt.edu,
        josef@redhat.com,
        Michael Monnerie <michael.monnerie@is.it-management.at>,
        Christoph Hellwig <hch@infradead.org>, linux-raid@vger.kernel.org,
        xfs@oss.sgi.com, linux-kernel@vger.kernel.org, dm-devel@redhat.com
Subject: Re: direct-io regression [Was: How to track down abysmal
 performance ata - raid1 - crypto - vg/lv - xfs]
Message-ID: <20100805190138.GV29846@think>
Mail-Followup-To: Chris Mason <chris.mason@oracle.com>,
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	Michael Monnerie <michael.monnerie@is.it-management.at>,
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References: <20100804085039.GA11671@infradead.org>
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 <20100804092122.GA2998@infradead.org>
 <20100804073546.GA7494@comet.dominikbrodowski.net>
 <201008041116.09822@zmi.at>
 <20100804102526.GB13766@isilmar-3.linta.de>
 <15446.1280953986@localhost>
 <20100805093100.GA3001@comet.dominikbrodowski.net>
 <20100805113240.GA29846@think>
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On Thu, Aug 05, 2010 at 02:58:37PM -0400, Jeff Moyer wrote:
> Chris Mason <chris.mason@oracle.com> writes:
> 
> > But, I'm surprised your drive is doing 8K dio reads at 16MB/s, that
> > seems a little high.  
> 
> I'm not sure why you think that.  We're talking about a plain old SATA
> disk, right?  I can get 40-50MB/s on my systems for 8KB O_DIRECT reads.
> What am I missing?

Clearly I'm wrong, his drive is going much faster ;)  I expect the
smaller reads to be slower but the drive's internal cache is doing well.

-chris