From: Pavel Machek Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible Date: Wed, 26 Aug 2009 01:29:35 +0200 Message-ID: <20090825232934.GG4300@elf.ucw.cz> References: <20090824212518.GF29763@elf.ucw.cz> <20090824223915.GI17684@mit.edu> <20090824230036.GK29763@elf.ucw.cz> <20090825000842.GM17684@mit.edu> <20090825094244.GC15563@elf.ucw.cz> <4A93E908.6050908@redhat.com> <20090825211515.GA3688@elf.ucw.cz> <4A9468E8.607@redhat.com> <20090825225114.GE4300@elf.ucw.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ric Wheeler , Theodore Tso , 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: david@lang.hm Return-path: Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:40996 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932288AbZHYX3m (ORCPT ); Tue, 25 Aug 2009 19:29:42 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: >>>> "ext3 works on flash and MD RAID5, as long as you do not have >>>> powerfail" seems to be the accurate statement, and if you don't need >>>> to protect against powerfails, you can just use ext2. >>> >>> Strange how your personal preference is totally out of sync with the >>> entire enterprise class user base. >> >> Perhaps noone told them MD RAID5 is dangerous? You see, that's exactly >> what I'm trying to document here. > > a MD raid array that's degraded to the point where there is no redundancy > is dangerous, but I don't think that any of the enterprise users would be > surprised. > > I think they will be surprised that it's possible that a prior failed > write that hasn't been scrubbed can cause data loss when the array later > degrades. Cool, so Ted's "raid5 has highly undesirable properties" is actually pretty accurate. Some raid person should write more detailed README, I'd say... Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html