From: Michael Tokarev <mjt@tls.msk.ru>
To: Maurice Hilarius <maurice@harddata.com>
Cc: linux-raid@vger.kernel.org
Subject: Re: Awful RAID5 random read performance
Date: Sun, 31 May 2009 10:25:42 +0400 [thread overview]
Message-ID: <4A2222E6.2070705@msgid.tls.msk.ru> (raw)
In-Reply-To: <4A21A938.6050907@harddata.com>
Maurice Hilarius wrote:
> A friend writes:
>
> On a recent machine set up with Raid5.
> On a AMD Phenom II X4 810, and 4GB ram.
> 4 Seagate 7200.12 SATA 1TB drives,
>
> I'm getting some rather impressive numbers for sequential read
> (300MB/s+) and write (170MB/s+) but the random read is proving to be
> absolutely atrocious.
> iostat says its going at about 0.5MB/s,
The key thing about random i/o is the block size. With, say, 512bytes
blocks and single thread you will see less than 0.5Mb/sec. With 64kbytes
blocksize it will be much better.
To diagnose: first try the same test on bare disk without raid layer.
Next try to vary block size and number of concurrent threads doing I/O.
There's no tweaks needed really.
/mjt
next prev parent reply other threads:[~2009-05-31 6:25 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-30 21:46 Awful RAID5 random read performance Maurice Hilarius
2009-05-31 6:25 ` Michael Tokarev [this message]
2009-05-31 7:47 ` Thomas Fjellstrom
2009-05-31 12:29 ` John Robinson
2009-05-31 15:41 ` Leslie Rhorer
2009-05-31 16:56 ` Thomas Fjellstrom
2009-05-31 18:26 ` Keld Jørn Simonsen
2009-06-02 18:54 ` Bill Davidsen
2009-06-02 19:47 ` Keld Jørn Simonsen
2009-06-02 23:13 ` John Robinson
2009-06-03 18:38 ` Bill Davidsen
2009-06-03 19:57 ` John Robinson
2009-06-03 22:21 ` Goswin von Brederlow
2009-06-04 11:23 ` Keld Jørn Simonsen
2009-06-04 22:40 ` Nifty Fedora Mitch
2009-06-06 23:06 ` Bill Davidsen
2009-06-01 1:19 ` Carlos Carvalho
2009-06-01 4:57 ` Leslie Rhorer
2009-06-01 5:39 ` Thomas Fjellstrom
2009-06-01 12:43 ` Maurice Hilarius
2009-06-02 14:57 ` Wil Reichert
2009-06-02 15:14 ` Maurice Hilarius
2009-06-02 19:47 ` Bill Davidsen
2009-06-01 11:41 ` Goswin von Brederlow
2009-06-03 1:57 ` Leslie Rhorer
2009-05-31 17:19 ` Goswin von Brederlow
2009-06-01 12:01 ` John Robinson
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