Date: Wed, 14 May 2003 10:27:38 +0930 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: The Hermit Hacker <scrappy@hub.org> Cc: freebsd-scsi@freebsd.org Subject: Re: RAID5 capacities / usable drive space ... Message-ID: <20030514005737.GA68496@wantadilla.lemis.com> In-Reply-To: <20030509222154.N728@hub.org> References: <20030509222154.N728@hub.org>
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--/04w6evG8XlLl3ft Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Friday, 9 May 2003 at 22:25:51 -0300, The Hermit Hacker wrote: > > I have someone telling me something that I'd never heard before, and find > difficult to believe ... > > Apparently, he is under the impression that altho a file system shows a > capacity of, say, 100G, its usable space is around 50% of that ... > anything higher then that, you risk problems ... (significantly reduced > MTBF of the drives, degradation in performance, etc) ... > > His opinion seems to be based on some talks he had with ppl at IBM and > Seagate way back in '89, but still seems to feel they are applicable today > ... > > Is there any fact behind his opinion? It's difficult to say if he hasn't specified reasons. I can think of a couple of possibilities. One would be, of course, that RAID-5 always has overhead for parity, and the other is the fact that file system performance deteriorates when the file system fills up (thus the 10% left over by UFS). None of these sound like good reasons, though. MTBF depends on the activity, not what kind of data (allocated/non-allocated) is on the drives. Greg -- See complete headers for address and phone numbers --/04w6evG8XlLl3ft Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.0 (FreeBSD) iD8DBQE+wZSBIubykFB6QiMRAnyHAJ9pALn6i2gMaJCteDEvzEYB7QO3QgCghnpR dqRg3kni7ux1rfKzdvwWEd4= =OpmP -----END PGP SIGNATURE----- --/04w6evG8XlLl3ft--
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