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Message-ID: <e2e108260803280044o1bf41e5q8fd0b00a772b54a4@mail.gmail.com>
Date: Fri, 28 Mar 2008 08:44:37 +0100
From: "Bart Van Assche" <bart.vanassche@gmail.com>
To: "Bill Davidsen" <davidsen@tmr.com>
Subject: Re: RAID-1 performance under 2.4 and 2.6
Cc: "Chris Snook" <csnook@redhat.com>,
       "Emmanuel Florac" <eflorac@intellique.com>,
       linux-kernel@vger.kernel.org
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On Thu, Mar 27, 2008 at 10:53 PM, Bill Davidsen <davidsen@tmr.com> wrote:
> Bart Van Assche wrote:
> > On Tue, Mar 25, 2008 at 11:00 PM, Chris Snook <csnook@redhat.com> wrote:
> >>  It means you shouldn't use dd as a benchmark.
> >
> > If you want to benchmark write speed, you should add
> > oflag=direct,dsync to the dd command line. For benchmarking read speed
> > you should specify iflag=direct. Or, even better, you can use xdd with
> > the flags -dio -processlock.
>
>  No, you want your benchmark to measure performance doing what the
>  application does. Do unless you have an application which has been
>  heavily Linux-ized you don't want to measure something unrelated to the
>  application requirements.

A basic fact I learned in science classes: if you measure something,
know very well what you measure and make sure your measurement is
repeatable. But it was some time ago I learned this. Maybe the whole
world changed since I learned that ?

Bart.
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