From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263378AbTJUVy2 (ORCPT ); Tue, 21 Oct 2003 17:54:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263382AbTJUVy2 (ORCPT ); Tue, 21 Oct 2003 17:54:28 -0400 Received: from tmr-02.dsl.thebiz.net ([216.238.38.204]:36868 "EHLO gatekeeper.tmr.com") by vger.kernel.org with ESMTP id S263378AbTJUVy0 (ORCPT ); Tue, 21 Oct 2003 17:54:26 -0400 To: linux-kernel@vger.kernel.org Path: gatekeeper.tmr.com!davidsen From: davidsen@tmr.com (bill davidsen) Newsgroups: mail.linux-kernel Subject: Re: Software RAID5 with 2.6.0-test Date: 21 Oct 2003 21:44:21 GMT Organization: TMR Associates, Schenectady NY Message-ID: References: <1065690658.10389.19.camel@slurv> <20031017192419.GG8711@unthought.net> X-Trace: gatekeeper.tmr.com 1066772661 19794 192.168.12.62 (21 Oct 2003 21:44:21 GMT) X-Complaints-To: abuse@tmr.com Originator: davidsen@gatekeeper.tmr.com Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org In article <20031017192419.GG8711@unthought.net>, Jakob Oestergaard wrote: | Now that I'm posting anyway - I thought of a plus for the HW RAID | controllers (hey, they're way behind on the scoreboard so far, so I | might as well be a gentleman and give them a point or two): | *) Battery backed write cache | | This will allow the controller to say 'ok I'm done with your sync()', | way before the data actually reaches the disk platters. For some | workloads this can be a big win. Unless the drives are battery backed up as well, I'm not sure that this is a good thing, or at least a safe thing. And if a write error happens after the controller tells you the sync() is done? That's a question, not a comment, I'm not sure Linux software RAID would relocate if the drive was out of spare sectors, either, but it at least could. I don't question your statement that caching helps performance, but I think there is some loss of reliability. I have no numbers to estimate the effect, so take it as a comment only. -- bill davidsen CTO, TMR Associates, Inc Doing interesting things with little computers since 1979.