Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755507AbYCZHP1 (ORCPT ); Wed, 26 Mar 2008 03:15:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751911AbYCZHPU (ORCPT ); Wed, 26 Mar 2008 03:15:20 -0400 Received: from fg-out-1718.google.com ([72.14.220.157]:28722 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751577AbYCZHPT (ORCPT ); Wed, 26 Mar 2008 03:15:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=XxFWPzwyxg7Bs8GmAC51+vZcSSWzX679YMEeFekRZ/i7p8ev7sKuDq+tfxwhyt3JMMRRnE8wdOuQWj04zxnzeTODFlbuYVCI5Osprq8EyBEgUJwPPzFsO9RQPGsVXDFksaqHWLg9EV8AYJAtAnAd35k+ovkXmNqCegYqOG3lQC8= Message-ID: Date: Wed, 26 Mar 2008 08:15:15 +0100 From: "Bart Van Assche" To: "Chris Snook" Subject: Re: RAID-1 performance under 2.4 and 2.6 Cc: "Emmanuel Florac" , linux-kernel@vger.kernel.org In-Reply-To: <47E975F8.3000702@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080325194306.4ac71ff2@galadriel.home> <47E975F8.3000702@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1907 Lines: 39 On Tue, Mar 25, 2008 at 11:00 PM, Chris Snook wrote: > Emmanuel Florac wrote: > > I post there because I couldn't find any information about this > > elsewhere : on the same hardware ( Athlon X2 3500+, 512MB RAM, 2x400 GB > > Hitachi SATA2 hard drives ) the 2.4 Linux software RAID-1 (tested 2.4.32 > > and 2.4.36.2, slightly patched to recognize the hardware :p) is way > > faster than 2.6 ( tested 2.6.17.13, 2.6.18.8, 2.6.22.16, 2.6.24.3) > > especially for writes. I actually made the test on several different > > machines (same hard drives though) and it remained consistent across > > the board, with /mountpoint a software RAID-1. > > Actually checking disk activity with iostat or vmstat shows clearly a > > cache effect much more pronounced on 2.4 (i.e. writing goes on much > > longer in the background) but it doesn't really account for the > > difference. I've also tested it thru NFS from another machine (Giga > > ethernet network): > > > > dd if=/dev/zero of=/mountpoint/testfile bs=1M count=1024 > > > > kernel 2.4 2.6 2.4 thru NFS 2.6 thru NFS > > > > write 90 MB/s 65 MB/s 70 MB/s 45 MB/s > > read 90 MB/s 80 MB/s 75 MB/s 65 MB/s > > > > Duh. That's terrible. Does it mean I should stick to (heavily > > patched...) 2.4 for my file servers or... ? :) > > 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. Bart. -- 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/