Date: Sat, 21 Aug 2004 18:16:12 +0930 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: freebsd-performance@FreeBSD.org Subject: Re: RAID-3? (was: cvs commit: src MAINTAINERS) Message-ID: <20040821084612.GH92256@wantadilla.lemis.com> In-Reply-To: <20040821083757.GE30151@darkness.comp.waw.pl> References: <20040817074633.GO30151@darkness.comp.waw.pl> <20040817112900.GA31635@freebie.xs4all.nl> <20040817124020.GK88156@wantadilla.lemis.com> <20040817131612.GT30151@darkness.comp.waw.pl> <20040819024359.GA85432@wantadilla.lemis.com> <20040820193547.GZ30151@darkness.comp.waw.pl> <20040820223446.GA18838@panzer.kdm.org> <20040821080614.GC30151@darkness.comp.waw.pl> <20040821083207.GG92256@wantadilla.lemis.com> <20040821083757.GE30151@darkness.comp.waw.pl>
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--7cm2iqirTL37Ot+N Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Saturday, 21 August 2004 at 10:37:57 +0200, Pawel Jakub Dawidek wrote: > On Sat, Aug 21, 2004 at 06:02:07PM +0930, Greg 'groggy' Lehey wrote: > +> On Saturday, 21 August 2004 at 10:06:14 +0200, Pawel Jakub Dawidek wrote: > +> > So as you can see there are no difference in reading (actually > +> > reading in degraded mode is even a bit faster, hard to say why). > +> > +> I would have half expected this. If you're reading parity as well, > +> then without spindle sync it will take longer for three I/Os to > +> complete than 2. > > I'm not sure if I understand you well... I think you understood what I said, but it looks like it was based on a misassumption. > In RAID3, when array is complete you don't use parity component for > reading at all. So in complete mode, as well as in degraded mode > RAID3 is using only two components for reading. OK, that seems reasonable. phk suggested that you would check parity on reads. Yes, in that case you'd expect things to be identical. Greg -- Note: I discard all HTML mail unseen. Finger grog@FreeBSD.org for PGP public key. See complete headers for address and phone numbers. --7cm2iqirTL37Ot+N Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.0 (FreeBSD) iD8DBQFBJwvUIubykFB6QiMRAg8xAKCKid9G6RFJEPAYsu10eU6W9PfciQCgopuP Qvwfa0eo4N+QOd6XItfv7JU= =dCEj -----END PGP SIGNATURE----- --7cm2iqirTL37Ot+N--
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