From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932783AbZHZKj3 (ORCPT ); Wed, 26 Aug 2009 06:39:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932694AbZHZKjW (ORCPT ); Wed, 26 Aug 2009 06:39:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34883 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932633AbZHZKjS (ORCPT ); Wed, 26 Aug 2009 06:39:18 -0400 Message-ID: <4A9510D2.1090704@redhat.com> Date: Wed, 26 Aug 2009 06:39:14 -0400 From: Ric Wheeler User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.1) Gecko/20090814 Fedora/3.0-2.6.b3.fc11 Lightning/1.0pre Thunderbird/3.0b3 MIME-Version: 1.0 To: Theodore Tso , Pavel Machek , Florian Weimer , Goswin von Brederlow , Rob Landley , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, corbet@lwn.net Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible References: <20090825225114.GE4300@elf.ucw.cz> <4A946DD1.8090906@redhat.com> <20090825232601.GF4300@elf.ucw.cz> <4A947682.2010204@redhat.com> <20090825235359.GJ4300@elf.ucw.cz> <4A947DA9.2080906@redhat.com> <20090826001645.GN4300@elf.ucw.cz> <4A948259.40007@redhat.com> <20090826010018.GA17684@mit.edu> <4A948C94.7040103@redhat.com> <20090826025849.GF32712@mit.edu> In-Reply-To: <20090826025849.GF32712@mit.edu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/25/2009 10:58 PM, Theodore Tso wrote: > On Tue, Aug 25, 2009 at 09:15:00PM -0400, Ric Wheeler wrote: > >> I agree with the whole write up outside of the above - degraded RAID >> does meet this requirement unless you have a second (or third, counting >> the split write) failure during the rebuild. >> > The argument is that if the degraded RAID array is running in this > state for a long time, and the power fails while the software RAID is > in the middle of writing out a stripe, such that the stripe isn't > completely written out, we could lose all of the data in that stripe. > > In other words, a power failure in the middle of writing out a stripe > in a degraded RAID array counts as a second failure. > > To me, this isn't a particularly interesting or newsworthy point, > since a competent system administrator who cares about his data and/or > his hardware will (a) have a UPS, and (b) be running with a hot spare > and/or will imediately replace a failed drive in a RAID array. > > - Ted > I agree that this is not an interesting (or likely) scenario, certainly when compared to the much more frequent failures that RAID will protect against which is why I object to the document as Pavel suggested. It will steer people away from using RAID and directly increase their chances of losing their data if they use just a single disk. Ric