Date: Mon, 15 Nov 1999 20:38:28 +0100 From: Bernd Walter <ticso@cicely.de> To: Greg Lehey <grog@lemis.com> Cc: Bernd Walter <ticso@cicely.de>, Mattias Pantzare <pantzer@ludd.luth.se>, freebsd-fs@FreeBSD.ORG Subject: Re: RAID-5 and failure Message-ID: <19991115203828.B5417@cicely7.cicely.de> In-Reply-To: <19991113213325.57908@mojave.sitaranetworks.com> References: <ticso@cicely.de> <199911061716.SAA20783@zed.ludd.luth.se> <19991106183316.A9420@cicely7.cicely.de> <19991113213325.57908@mojave.sitaranetworks.com>
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On Sat, Nov 13, 1999 at 09:33:25PM -0500, Greg Lehey wrote: > > 4. The system crashes after writing the first data block for a RAID-5 > stripe and before writing the last data block. > > When the system comes up, both data and parity are inconsistent. > > 5. The system crashes after writing the last data block for a RAID-5 > stripe and before writing the last parity block. > > When the system comes up, data is consistent, and parity is > inconsistent. > > There are a number of ways of dealing with situations 4 and 5. The > real problem is that they only occur when the system crashes, so > whatever recovery information is required must be stored in > non-volatile storage. Some systems do include a NOVRAM for this kind > of information, but in general purpose systems the only possibility is > to write the information to disk, which would make the inherently slow > RAID-5 write even slower. My attitude here is that RAID-5 writes are > comparatively infrequent, and so are crashes. In the case of (5), you > could rebuild parity after a crash. In the case of (4), I have no > good answer. Suggestions welcome. Case 4 is not that different from case 5 as any differences should be handled by the FS using the volume. -- B.Walter COSMO-Project http://www.cosmo-project.de ticso@cicely.de Usergroup info@cosmo-project.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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