From: david@lang.hm Subject: Re: [patch] ext2/3: document conditions when reliable operation is possible Date: Tue, 25 Aug 2009 16:03:18 -0700 (PDT) Message-ID: References: <20090824205209.GE29763@elf.ucw.cz> <4A930160.8060508@redhat.com> <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; format=flowed 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: Pavel Machek Return-path: Received: from mail.lang.hm ([64.81.33.126]:39378 "EHLO bifrost.lang.hm" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932215AbZHYXEO (ORCPT ); Tue, 25 Aug 2009 19:04:14 -0400 In-Reply-To: <20090825225114.GE4300@elf.ucw.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 26 Aug 2009, Pavel Machek wrote: >>>> I don't object to making that general statement - "Don't hot unplug a >>>> device with an active file system or actively used raw device" - but >>>> would object to the overly general statement about ext3 not working on >>>> flash, RAID5 not working, etc... >>> >>> You can object any way you want, but running ext3 on flash or MD RAID5 >>> is stupid: >>> >>> * ext2 would be faster >>> >>> * ext2 would provide better protection against powerfail. >> >> Not true in the slightest, you continue to ignore the ext2/3/4 developers >> telling you that it will lose data. > > I know I will lose data. Both ext2 and ext3 will lose data on > flashdisk. (That's what I'm trying to document). But... what is the > benefit of ext3 journaling on MD RAID5? (On flash, ext3 at least > protects you against kernel panic. MD RAID5 is in software, so... that > additional protection is just not there). the block device can loose data, it has absolutly nothing to do with the filesystem >>> "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. David Lang