From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262429AbTJGQAJ (ORCPT ); Tue, 7 Oct 2003 12:00:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262436AbTJGQAI (ORCPT ); Tue, 7 Oct 2003 12:00:08 -0400 Received: from h68-147-142-75.cg.shawcable.net ([68.147.142.75]:49145 "EHLO schatzie.adilger.int") by vger.kernel.org with ESMTP id S262429AbTJGQAA (ORCPT ); Tue, 7 Oct 2003 12:00:00 -0400 Date: Tue, 7 Oct 2003 09:59:37 -0600 From: Andreas Dilger To: Nikita Danilov Cc: "E. Gryaznova" , linux-kernel@vger.kernel.org Subject: Re: Can dbench be used for benchmarking fs? Message-ID: <20031007095937.A1593@schatzie.adilger.int> Mail-Followup-To: Nikita Danilov , "E. Gryaznova" , linux-kernel@vger.kernel.org References: <3F82B4C6.707221A@namesys.com> <20031007082944.D1564@schatzie.adilger.int> <16258.53615.17755.970961@laputa.namesys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: <16258.53615.17755.970961@laputa.namesys.com>; from Nikita@Namesys.COM on Tue, Oct 07, 2003 at 06:45:03PM +0400 X-GPG-Key: 1024D/0D35BED6 X-GPG-Fingerprint: 7A37 5D79 BF1B CECA D44F 8A29 A488 39F5 0D35 BED6 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Oct 07, 2003 18:45 +0400, Nikita Danilov wrote: > Andreas Dilger writes: > > On Oct 07, 2003 16:42 +0400, E. Gryaznova wrote: > > > I use dbench for benchmarking the file systems and some results are > > > suspicious for me. > > > : > > > : > > > : > > > As the result: the measuring deviation is equal = 23.4062 - 15.7005 = > > > 7.7057 or about ~38% from average value. > > > > > > So, I have 2 questions : > > > 1. Is there a way to avoid such big deviations on measuring a file > > > systems throughput and to get more stable results? > > > 2. Can dbench be used for benchmarking the file systems and if it is so > > > -- what is the predictable error on the measuring? > > > > Dbench is not a good filesystem benchmark, because it deletes all of the > > files at the end. Use something else for the filesystem benchmark - there > > Err... What is wrong with deleting all files at the end? Or do you mean > it should mix file operations during run? > > > are lots of them (bonnie, iozone, mongo, etc). > > But why variance is so large? Dbench is a bad filesystem benchmark because if all (or some large part) of the files are deleted before the VM flushes them to disk, then you are not really testing filesystem performance very much. If you have enough RAM in your system and a fast enough CPU you could complete the entire dbench run without ever writing any data to disk. There is some filesystem activity (you need to create files and map pages), but it isn't a good test of filesystem throughput. The reason there is so much variability in the tests is that if the test takes even a small amount more time to run this means more data gets flushed to disk by the VM (instead of being deleted and never written), making the test run longer and even _more_ data needs to get written, etc. Dbench is a good multi-threaded filesystem stress program, but it isn't a good benchmark. Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/