Date: Tue, 13 May 2003 22:13:45 -0300 (ADT) From: "Marc G. Fournier" <scrappy@hub.org> To: Greg 'groggy' Lehey <grog@FreeBSD.org> Cc: freebsd-scsi@freebsd.org Subject: Re: RAID5 capacities / usable drive space ... Message-ID: <20030513220947.L3557@hub.org> In-Reply-To: <20030514005737.GA68496@wantadilla.lemis.com> References: <20030509222154.N728@hub.org> <20030514005737.GA68496@wantadilla.lemis.com>
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'K ... I'm going to be setting up a server to test my knowledge here, but, I've had someone tell me: "the fact that you need a minimum of three drives in Raid 5, so a three drive configuration in Raid5 is not hot swappable nor will it boot with less than three working drives." .... My understanding was that if I had three drives in a RAID5 configuration, and one died, the file system would still function with the 2 drives ... Thanks ... On Wed, 14 May 2003, Greg 'groggy' Lehey wrote: > 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 >
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