From: Pavel Machek Subject: Re: raid is dangerous but that's secret (was Re: [patch] ext2/3: Date: Mon, 31 Aug 2009 13:04:48 +0200 Message-ID: <20090831105645.GD1353@ucw.cz> References: <20090831005426.13607.qmail@science.horizon.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: George Spelvin Return-path: Content-Disposition: inline In-Reply-To: <20090831005426.13607.qmail@science.horizon.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.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