From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751896AbZHaLE6 (ORCPT ); Mon, 31 Aug 2009 07:04:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751798AbZHaLE5 (ORCPT ); Mon, 31 Aug 2009 07:04:57 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:38496 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbZHaLE4 (ORCPT ); Mon, 31 Aug 2009 07:04:56 -0400 Date: Mon, 31 Aug 2009 13:04:48 +0200 From: Pavel Machek To: George Spelvin Cc: linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: raid is dangerous but that's secret (was Re: [patch] ext2/3: Message-ID: <20090831105645.GD1353@ucw.cz> References: <20090831005426.13607.qmail@science.horizon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090831005426.13607.qmail@science.horizon.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! > Actually, there is something the file system can do to make journaling > safe on degraded RAIDs: make the (checksummed) journal blocks equal to > the RAID stripe size. Or, equivalently, pad out to the RAID stripe > size each commit. > > This sometimes leads to awkward block sizes, but while writing > to any *one* stripe on a degraded RAID-5 endangers the others, you > can write to *all* of them with the usual semantics. Well, that would work... but you'd also have to journal data, with the same block size. Not exactly fast, but at least safe... > That's one thing I really like about ZFS: its policy of "don't trust > the disks." If nothing else, simply telling you "your disks f*ed up, > and I caught them doing it", instead of the usual mysterious corruption > detectec three months later, is tremendoudly useful information. The more I learn about storage, the more I like idea of zfs. Given the subtle issues between filesystem and raid layer, integrating them just makes sense. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html