From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932295AbWGGTwm (ORCPT ); Fri, 7 Jul 2006 15:52:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932299AbWGGTwm (ORCPT ); Fri, 7 Jul 2006 15:52:42 -0400 Received: from thunk.org ([69.25.196.29]:46750 "EHLO thunker.thunk.org") by vger.kernel.org with ESMTP id S932295AbWGGTwl (ORCPT ); Fri, 7 Jul 2006 15:52:41 -0400 Date: Fri, 7 Jul 2006 15:52:23 -0400 From: Theodore Tso To: Bill Davidsen Cc: Trond Myklebust , "J. Bruce Fields" , Thomas Glanzmann , LKML Subject: Re: ext4 features Message-ID: <20060707195223.GA12301@thunk.org> Mail-Followup-To: Theodore Tso , Bill Davidsen , Trond Myklebust , "J. Bruce Fields" , Thomas Glanzmann , LKML 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44ADC3CE.1030302@tmr.com> User-Agent: Mutt/1.5.11 X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on thunker.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 06, 2006 at 10:15:42PM -0400, 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. Not four times a day, but probably once a month or two it would be a *very* good idea to do periodic sweeps of files to make sure the hard drive hasn't corrupted the files out from under you. If you have 20+ TB of data, the probability of silent data corruption starts going up. That would be justification for storing the checksum in the inode or in the EA of the file, with the kernel automatically clearing it if the file was *deliberately* changed. The goal is to detect the disk silently changing the data for you, free of charge.... - Ted