From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030299AbWGFPT4 (ORCPT ); Thu, 6 Jul 2006 11:19:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030324AbWGFPTz (ORCPT ); Thu, 6 Jul 2006 11:19:55 -0400 Received: from mexforward.lss.emc.com ([128.222.32.20]:38452 "EHLO mexforward.lss.emc.com") by vger.kernel.org with ESMTP id S1030299AbWGFPTz (ORCPT ); Thu, 6 Jul 2006 11:19:55 -0400 Message-ID: <44AD286F.3030507@emc.com> Date: Thu, 06 Jul 2006 11:12:47 -0400 From: Ric Wheeler Reply-To: ric@emc.com User-Agent: Mozilla Thunderbird 1.0.7 (X11/20050923) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Tomasz Torcz CC: Thomas Glanzmann , "Theodore Ts'o" , LKML Subject: Re: ext4 features References: <20060701163301.GB24570@cip.informatik.uni-erlangen.de> <20060701170729.GB8763@irc.pl> <20060701174716.GC24570@cip.informatik.uni-erlangen.de> <20060701181702.GC8763@irc.pl> In-Reply-To: <20060701181702.GC8763@irc.pl> 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: 2006.7.6.75432 X-PerlMx-Spam: Gauge=, SPAM=2%, Reasons='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 Tomasz Torcz wrote: >On Sat, Jul 01, 2006 at 07:47:16PM +0200, Thomas Glanzmann wrote: > > >>Hello, >> >> >>>Checksums are not very useful for themselves. They are useful when we >>>have other copy of data (think raid mirroring) so data can be >>>reconstructed from working copy. >>> >>> >>it would be possible to identify data corruption. >> >> > > Yes, but what good is identification? We could only return I/O error. >Ability to fix corruption (like ZFS) is the real killer. > > Having a checksum (or even a digital signature on a file) that lets us detect corruption is very useful since, in many cases, it allows us to flag the file as corrupt before it gets used. In some cases, this is a big hint that you should restore it from backup (tape, other disk, etc). I think that it is a generally useful thing even when not on a self correcting device, ric