From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751150AbWGGCmz (ORCPT ); Thu, 6 Jul 2006 22:42:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751151AbWGGCmz (ORCPT ); Thu, 6 Jul 2006 22:42:55 -0400 Received: from mexforward.lss.emc.com ([128.222.32.20]:24967 "EHLO mexforward.lss.emc.com") by vger.kernel.org with ESMTP id S1751150AbWGGCmz (ORCPT ); Thu, 6 Jul 2006 22:42:55 -0400 Message-ID: <44ADCA0C.90401@emc.com> Date: Thu, 06 Jul 2006 22:42:20 -0400 From: Ric Wheeler User-Agent: Mozilla Thunderbird 1.0.7 (X11/20050923) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Bill Davidsen CC: Trond Myklebust , "J. Bruce Fields" , Theodore Tso , Thomas Glanzmann , LKML Subject: Re: ext4 features References: <20060701163301.GB24570@cip.informatik.uni-erlangen.de> <20060704010240.GD6317@thunk.org> <44ABAF7D.8010200@tmr.com> <20060705125956.GA529@fieldses.org> <44AC2B56.8010703@tmr.com> <20060705214133.GA28487@fieldses.org> <44AC7647.2080005@tmr.com> <1152189796.5689.17.camel@lade.trondhjem.org> <44ADC3CE.1030302@tmr.com> In-Reply-To: <44ADC3CE.1030302@tmr.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-PMX-Version: 4.7.1.128075, Antispam-Engine: 2.4.0.264935, Antispam-Data: 2006.7.6.191432 X-PerlMx-Spam: Gauge=, SPAM=2%, Reason='EMC_FROM_0+ -2, __CT 0, __CTE 0, __CT_TEXT_PLAIN 0, __HAS_MSGID 0, __MIME_TEXT_ONLY 0, __MIME_VERSION 0, __SANE_MSGID 0, __USER_AGENT 0' Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Bill Davidsen wrote: > Trond Myklebust wrote: > >> Nobody gives a rats arse about backups: those are infrequent and >> can/should use more sophisticated techniques such as checksumming. >> > Actually, those of us who do run production servers care vastly about > backups. And beside being utterly unscalable (checksum 20 TB of files > four times a day to find what changed???), you would have to remember > the checksums for all those files. > The point of using checksums (or digital signatures on files) is to be able to detect when the on disk file has been corrupted - not to look for updates. With normal disks, even writes that are flagged as correct will occasionally actually end up corrupt on disk. The rate that you need to validate the checksums is not at a 4 time a day rate. Buying a nice, high array can make this much less of a concern, but those of us who get stuck using commodity disks should always have a way of detecting corruption and a backup (either on tape or on another box). ric