Date: Sun, 6 May 2001 13:03:47 +0930 From: Greg Lehey <grog@lemis.com> To: Bob Greene <rgreene@tclme.org> Cc: "Andrew C. Hornback" <hornback@wireco.net>, Steve Blanzy <sblanzy@aperion.com>, FreeBSD Questions <questions@FreeBSD.ORG> Subject: Re: Raid Message-ID: <20010506130347.F39554@wantadilla.lemis.com> In-Reply-To: <3AF4BF5A.A03D7278@tclme.org>; from rgreene@tclme.org on Sat, May 05, 2001 at 10:04:58PM -0500 References: <000a01c0d57f$2158bb40$0400a8c0@192.168.0.1> <000701c0d581$3dd2da60$0e00000a@tomcat> <20010506101618.B39554@wantadilla.lemis.com> <3AF4BF5A.A03D7278@tclme.org>
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On Saturday, 5 May 2001 at 22:04:58 -0500, Bob Greene wrote: > Greg Lehey wrote: >> >> No, RAID-1 gives you the best performance of any RAID setup. The >> reason why you need at least 3 disks for RAID-5 is because it is >> slower, and though it would theoretically work with only two disks, >> it has no advantages over RAID-1 in this configuration. >> > > Huh? This paragraph makes no sense. > > RAID 0 = striped set > RAID 1 = mirrored set > RAID 5 = striped set with parity > > RAID 1 gives maximum redundancy, at the cost of two writes. The third > disk in RAID 5 is not a consequence of performance, it's a requirement > for redundancy. RAID 5 with only 2 disks is a failure condition of a 3 > disk array. At that point it's effectively just a striped set. No, because in degraded 3-disk RAID-5 every third access is intended for the failed drive. In order to read that data, you need to read both (all) the other drives and reconstruct it. This can be very slow if you have a large number of drives in the set. Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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