linux-ext4 - Re: More testing: 4x parallel 2G writes, sequential reads

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Message-ID: <20071108001434.GB16884@yzf.shaptech.com>
Date:	Wed, 7 Nov 2007 16:14:34 -0800
From:	Shapor Naghibzadeh <shapor@...por.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: More testing: 4x parallel 2G writes, sequential reads

On Wed, Nov 07, 2007 at 04:42:59PM -0600, Eric Sandeen wrote:
> Again this was on a decent HW raid so seek penalties are probably not
> too bad.

You may want to verify that by doing a benchmark on the raw device.  I
recently did some benchmarks doing random I/O on a Dell 2850 w/ a PERC
(megaraid) RAID5 w/ 128MB onboard writeback cache and 6x 15krpm drives
and noticed appoximately one order of magnitude throughput drop on
small (stripe-sized) random reads versus linear.  It maxed out at ~100
random read IOPs or "seeks/sec" (suprisingly low).

Out of curiousity, how are you counting the seeks?

Shapor
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