Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965370AbXATUTv (ORCPT ); Sat, 20 Jan 2007 15:19:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965369AbXATUTv (ORCPT ); Sat, 20 Jan 2007 15:19:51 -0500 Received: from 1wt.eu ([62.212.114.60]:2091 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965373AbXATUTv (ORCPT ); Sat, 20 Jan 2007 15:19:51 -0500 Date: Sat, 20 Jan 2007 21:19:23 +0100 From: Willy Tarreau To: Ismail =?iso-8859-1?Q?D=F6nmez?= Cc: Tim Schmielau , linux-kernel@vger.kernel.org Subject: Re: Abysmal disk performance, how to debug? Message-ID: <20070120201923.GC25307@1wt.eu> References: <200701201920.54620.ismail@pardus.org.tr> <200701201952.54714.ismail@pardus.org.tr> <200701202216.16637.ismail@pardus.org.tr> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <200701202216.16637.ismail@pardus.org.tr> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1407 Lines: 37 On Sat, Jan 20, 2007 at 10:16:15PM +0200, Ismail D?nmez wrote: > 20 Oca 2007 Cts 22:10 tarihinde, Tim Schmielau ??unlar?? yazm????t??: > [...] > > > > Note that these dd "benchmarks" are completely bogus, because the data=20 > > doesn't actually get written to disk in that time. For some enlightening=20 > > data, try > > > > time dd if=3D/dev/zero of=3D/tmp/1GB bs=3D1M count=3D1024; time sync > > > > The dd returns as soon as all data could be buffered in RAM. Only sync=20 > > will show how long it takes to actually write out the data to disk. > > also explains why you see better results is writeout starts earlier. > > Still not that bad: > > [~]> time dd if=/dev/zero of=/tmp/1GB bs=1M count=1024;sync > 1024+0 records in > 1024+0 records out > 1073741824 bytes (1,1 GB) copied, 53,3194 s, 20,1 MB/s > > real 0m53.517s > user 0m0.003s > sys 0m3.193s No, your measure is wrong because time measures "dd" and sync is done after. Either use Tim's method (time sync) or the one I proposed in previous mail (time dd | sync). Anyway, in your situation with a very small buffer, this should not change by more than half a second or so. Willy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/