From owner-freebsd-chat Fri Sep 29 11:10:59 2000 Delivered-To: freebsd-chat@freebsd.org Received: from hand.dotat.at (hand.dotat.at [212.240.134.135]) by hub.freebsd.org (Postfix) with ESMTP id CADA837B505 for ; Fri, 29 Sep 2000 11:10:33 -0700 (PDT) Received: from fanf by hand.dotat.at with local (Exim 3.15 #3) id 13f4bn-0000se-00; Fri, 29 Sep 2000 18:10:07 +0000 Date: Fri, 29 Sep 2000 18:10:07 +0000 From: Tony Finch To: Terry Lambert Cc: John Sconiers , Brad Knowles , Johann Visagie , chat@FreeBSD.ORG Subject: Re: SGI releases XFS under GPL Message-ID: <20000929181007.A3345@hand.dotat.at> References: <200009290115.SAA06192@usr05.primenet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2i In-Reply-To: <200009290115.SAA06192@usr05.primenet.com> Organization: Covalent Technologies, Inc Sender: owner-freebsd-chat@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Terry Lambert wrote: > >A common misconception about soft updates is that you can get >the same failure recovery that you would get from journalling >or logging. [...] > >The flaw with this theory is that a power failure is not the >only type of crash you could have, and running after any >crash that can corrupt any portion of the disk (e.g. most >disks corrupt sectors if power is lost during a write, and >in the evnt of a kernel panic, you don't know what data was >corrupted in core, then erroneously written to disk before >the actual panic, etc.), puts you at risk of further disk >corruption and user space software failures. In the worst >case, the crash was the result of a hardware failure of the >disk subsystem (disk, controller, cables, terminator, etc.). >So it is impossible to recover without an exterior log of >the events leading up to the crash (this is how the WAFL >file system from Network Appliance works: it uses an NVRAM >intention log). I'm not sure this argument is entirely sound: it also applies to journalling filesystems where the log is kept on disk. Even if the journal isn't on disk (the WAFL case) you can still be vulnerable to hardware failures -- I've heard of a NetApp becoming completely unusable after a disk decided to fail silently, the only way to recover being to copy the parts of the filesystem that didn't crash the NetApp to another machine. Tony. -- en oeccget g mtcaa f.a.n.finch v spdlkishrhtewe y dot@dotat.at eatp o v eiti i d. fanf@covalent.net To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message