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Date: Fri, 28 Mar 2008 08:44:37 +0100 From: "Bart Van Assche" <bart.vanassche@...il.com> To: "Bill Davidsen" <davidsen@....com> Cc: "Chris Snook" <csnook@...hat.com>, "Emmanuel Florac" <eflorac@...ellique.com>, linux-kernel@...r.kernel.org Subject: Re: RAID-1 performance under 2.4 and 2.6 On Thu, Mar 27, 2008 at 10:53 PM, Bill Davidsen <davidsen@....com> wrote: > Bart Van Assche wrote: > > On Tue, Mar 25, 2008 at 11:00 PM, Chris Snook <csnook@...hat.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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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