Date: Wed, 18 Aug 2004 23:28:48 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: "Greg 'groggy' Lehey" <grog@FreeBSD.org> Cc: Wilko Bulte <wb@freebie.xs4all.nl> Subject: Re: RAID-3? Message-ID: <20040819062848.GM99980@funkthat.com> In-Reply-To: <20040819062228.GO85432@wantadilla.lemis.com> References: <41449.1092750244@critter.freebsd.dk> <200408161043.i7GAhfXs079045@repoman.freebsd.org> <20040817004407.GA81257@wantadilla.lemis.com> <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> <41244217.6010102@samsco.org> <20040819062228.GO85432@wantadilla.lemis.com>
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Greg 'groggy' Lehey wrote this message on Thu, Aug 19, 2004 at 15:52 +0930:
> > Your quoted text also seems a bit subjective as there are very valid
> > reasons for RAID-3, especially if one is looking for consistent
> > low-latency transactions like in video recorders and servers.
>
> Well, I did use *exactly* this example. I also pointed out that the
> relative performance of modern disk subsystems is adequate for a
> single streaming video channel.
>
> Low latency depends on the number of concurrent accesses. RAID-3
> handles concurrent access poorly, exactly because it accesses all
> disks for each transfer.
One thing that RAID-3 has is that you never have to do a READ/MODIFY
cycle when you do writes. Until we implement a write-through cache
geom module, raid-5 will continue to substandard performance.
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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