Date: Thu, 19 Aug 2004 16:08:43 +0930 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: John-Mark Gurney <gurney_j@resnet.uoregon.edu> Cc: Wilko Bulte <wb@freebie.xs4all.nl> Subject: Re: RAID-3? Message-ID: <20040819063843.GP85432@wantadilla.lemis.com> In-Reply-To: <20040819062848.GM99980@funkthat.com> References: <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> <20040819062848.GM99980@funkthat.com>
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--XFI+TFG+M3u0jUjZ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wednesday, 18 August 2004 at 23:28:48 -0700, John-Mark Gurney wrote: > 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. Even then, RAID-5 might have higher bandwidth under some circumstances. My real question about RAID-3 remains: what use is it? This isn't nit-picking, it's certainly not a criticism of pjd. I just don't see any practical use on FreeBSD machines. Greg -- Note: I discard all HTML mail unseen. Finger grog@FreeBSD.org for PGP public key. See complete headers for address and phone numbers. --XFI+TFG+M3u0jUjZ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.0 (FreeBSD) iD8DBQFBJErzIubykFB6QiMRAjElAKCV0zZKDIz+kktS4IN+5ZFplWKvpACeO3ps lDZBSYVE/r5wu7KkEPb2MvE= =/OdA -----END PGP SIGNATURE----- --XFI+TFG+M3u0jUjZ--
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