Date: Thu, 19 Aug 2004 16:19:26 +0930 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: Wilko Bulte <wb@freebie.xs4all.nl> Subject: Re: RAID-3? Message-ID: <20040819064926.GQ85432@wantadilla.lemis.com> In-Reply-To: <11555.1092897238@critter.freebsd.dk> References: <20040819062228.GO85432@wantadilla.lemis.com> <11555.1092897238@critter.freebsd.dk>
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--yPSgZSQ6mfPWgZ9n Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thursday, 19 August 2004 at 8:33:58 +0200, Poul-Henning Kamp wrote: > In message <20040819062228.GO85432@wantadilla.lemis.com>, "Greg 'groggy' Lehey" > writes: >> On Thursday, 19 August 2004 at 0:00:55 -0600, Scott Long wrote: >>> >>> I think that you're really reading far too much into this. >> >> That depends on whether you care about accurate terminology or not. >> Or maybe it's you who is reading too much into the matter. > > I think being accurate is a great thing, but accuracy of definition > should never get in the way of working code. Agreed. I don't think it is. > The main features of RAID3 are the always full stripe access which > keeps your disk heads running in tandem which has desirable > performance characteristica. ... for single accessors. But a single IDE drive nowadays can transfer 40 MB a second. A 5 disk RAID-3 array should thus be able to transfer 160 MB a second. What do you need that for? > Also the fact that you can trivially add ECC instead of mere parity > is a big plus. Ah, but that would be RAID-2. Or something similar. > Raid5 with two bit ECC (sometimes called raid6) I thought RAID-6 was RAID-5 with two identical parity disks. Not so? > is a royal nightmare to code (see the raidframe paper) Does this define RAID-6, or just describe the pain? > whereas RAID3 in 4+2 or 8+3 is pretty trivial because of the > full-stripe access pattern. Sure, easy coding is good. And having written a RAID-5 implementation, I can believe what a nightmare that an ECC version might provide. > Now, can we stop the definition-thumbing and let Pawel work on his > code ? If need be, put this on your bumper-sticker: > > If you don't like RAID3 then don't use it! No, I think that's too simplistic. I don't see anybody stopping Pawel from doing what he wants. It would be nice to know why, though. Greg -- Note: I discard all HTML mail unseen. Finger grog@FreeBSD.org for PGP public key. See complete headers for address and phone numbers. --yPSgZSQ6mfPWgZ9n Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.0 (FreeBSD) iD8DBQFBJE12IubykFB6QiMRArhBAJoC/XwCTJmG2eVM4RWeau7PNh1zggCgrLhf Kq9UttrvNPevg/4v821rJkg= =t7Ee -----END PGP SIGNATURE----- --yPSgZSQ6mfPWgZ9n--
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