Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757505AbYCZIIs (ORCPT ); Wed, 26 Mar 2008 04:08:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752253AbYCZIId (ORCPT ); Wed, 26 Mar 2008 04:08:33 -0400 Received: from smtp7-g19.free.fr ([212.27.42.64]:58782 "EHLO smtp7-g19.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751297AbYCZIIb convert rfc822-to-8bit (ORCPT ); Wed, 26 Mar 2008 04:08:31 -0400 Date: Wed, 26 Mar 2008 09:05:27 +0100 From: Emmanuel Florac To: Bill Davidsen Cc: Chris Snook , linux-kernel@vger.kernel.org Subject: Re: RAID-1 performance under 2.4 and 2.6 Message-ID: <20080326090527.42286e8e@galadriel.home> In-Reply-To: <47E98DE4.9000906@tmr.com> References: <20080325194306.4ac71ff2@galadriel.home> <47E975F8.3000702@redhat.com> <47E98108.9000906@tmr.com> <47E98712.6090203@redhat.com> <47E98DE4.9000906@tmr.com> Organization: Intellique X-Mailer: Claws Mail 2.9.1 (GTK+ 2.8.20; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1273 Lines: 26 Le Tue, 25 Mar 2008 19:42:28 -0400 vous ?criviez: > And this is what I was saying earlier, there is a trend to blame the > benchmark when in fact the same benchmark runs well on 2.4. As I mentioned, it looks like 2.4 actually buffers write data on RAID-1 which is inherently bad (after all if I do RAID-1 it's for the sake of data integrity, and write caching just counters that). However, how bad dd may be, it reflects broadly my problem : on small systems using software RAID, IO is overall way better with 2.4 than 2.6, especially NFS thruput. Though I can substantially enhance 2.6 performance through tweaking (playing with read ahead, disk queue length etc), it still lags behind 2.4 with defaults settings by a clear margin (10% or more). This isn't true - fortunately - of larger systems with 12, 24, 48 disks drives, hardware RAID, Fibre Channel and al. -- -------------------------------------------------- Emmanuel Florac www.intellique.com -------------------------------------------------- -- 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/