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

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Message-ID: <47327D4C.7070604@redhat.com>
Date:	Wed, 07 Nov 2007 21:06:52 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Shapor Naghibzadeh <shapor@...por.com>
CC:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: More testing: 4x parallel 2G writes, sequential reads

Shapor Naghibzadeh wrote:
> 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?

Chris Mason's seekwatcher (google can find it for you) is doing the
graphing, it uses blocktrace for the raw data.

-Eric

> Shapor

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