From: Theodore Tso Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible Date: Tue, 25 Aug 2009 22:58:49 -0400 Message-ID: <20090826025849.GF32712@mit.edu> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: 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 To: Ric Wheeler Return-path: Received: from thunk.org ([69.25.196.29]:56502 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751697AbZHZC7C (ORCPT ); Tue, 25 Aug 2009 22:59:02 -0400 Content-Disposition: inline In-Reply-To: <4A948C94.7040103@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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