From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754806AbYC1MDV (ORCPT ); Fri, 28 Mar 2008 08:03:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752941AbYC1MDN (ORCPT ); Fri, 28 Mar 2008 08:03:13 -0400 Received: from mail.tmr.com ([64.65.253.246]:51726 "EHLO gaimboi.tmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753432AbYC1MDM (ORCPT ); Fri, 28 Mar 2008 08:03:12 -0400 Message-ID: <47ECDED6.4050100@tmr.com> Date: Fri, 28 Mar 2008 08:04:38 -0400 From: Bill Davidsen Organization: TMR Associates Inc, Schenectady NY User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061105 SeaMonkey/1.0.6 MIME-Version: 1.0 To: Bart Van Assche CC: Chris Snook , Emmanuel Florac , linux-kernel@vger.kernel.org Subject: Re: RAID-1 performance under 2.4 and 2.6 References: <20080325194306.4ac71ff2@galadriel.home> <47E975F8.3000702@redhat.com> <47EC173F.4050309@tmr.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Bart Van Assche wrote: > On Thu, Mar 27, 2008 at 10:53 PM, Bill Davidsen wrote: > >> Bart Van Assche wrote: >> >>> On Tue, Mar 25, 2008 at 11:00 PM, Chris Snook 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 ? > Sounds like we're saying the same thing. For naive applications dd is probably a closer model without direct or fconv, while if you want to see what you could gain using additional features those are useful options. I believe Chris was talking about the max speed possible, which is a good thing to know but not similar to simple programming or shell scripts using sed, grep, etc. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark