Date: Wed, 17 Nov 1999 19:19:13 +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: <19991117191912.A12883@cicely7.cicely.de> In-Reply-To: <19991116204101.12932@mojave.sitaranetworks.com> References: <ticso@cicely.de> <199911061716.SAA20783@zed.ludd.luth.se> <19991106183316.A9420@cicely7.cicely.de> <19991113213325.57908@mojave.sitaranetworks.com> <19991115203828.B5417@cicely7.cicely.de> <19991115145200.09633@mojave.sitaranetworks.com> <19991115210607.A6252@cicely7.cicely.de> <19991116204101.12932@mojave.sitaranetworks.com>
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On Tue, Nov 16, 1999 at 08:41:01PM -0500, Greg Lehey wrote: > On Monday, 15 November 1999 at 21:06:08 +0100, Bernd Walter wrote: > > > The FS should realy be able to handle this case as it knows that > > there is an outstanding write operation. > > How does it know? That's the question. All state information has > gone to /dev/null. The only alternative is to write this state > information to some non-volatile location, which usually means disk > and associated severe loss of performance. The FS is dirty. The FS before the panic/powerfailure/... had known the outstanding transaction and shouldn't create a situation in which fsck can't handle such a case. It should even expect only a part to be writen as multiple sector transfers are known not to be atomic - that's why critical state information should never cross sector boundarys. I asume most modern HDDs are able to finish a single sector write in case of power failures. In case the drive simply returns a CRC error we realy have a problem because the parity might not be in sync and we can't recover this sector relyable. Nevertheless I got several powerfailures during write access and never got CRCs since ESDI because of that. In case application data was lost that's not a OS specific problem. As long as the applications did not flush the buffers and success was returned it should not be surprised if data gets lost because they could also be in some kind of writecache. -- 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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