From owner-cvs-src@FreeBSD.ORG Thu Aug 19 06:59:05 2004 Return-Path: Delivered-To: cvs-src@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id C872216A4CE; Thu, 19 Aug 2004 06:59:05 +0000 (GMT) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id 28BD643D41; Thu, 19 Aug 2004 06:59:05 +0000 (GMT) (envelope-from scottl@samsco.org) Received: from [192.168.2.73] (cpe.125.wat.v126.packetworks.net [64.235.97.125] (may be forged)) (authenticated bits=0) by pooker.samsco.org (8.12.11/8.12.10) with ESMTP id i7J6xW3v067516; Thu, 19 Aug 2004 00:59:33 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <41244F17.9030007@samsco.org> Date: Thu, 19 Aug 2004 00:56:23 -0600 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.1) Gecko/20040801 X-Accept-Language: en-us, en MIME-Version: 1.0 To: "Greg 'groggy' Lehey" References: <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> <20040819063843.GP85432@wantadilla.lemis.com> <20040819064401.GN99980@funkthat.com> <20040819065155.GR85432@wantadilla.lemis.com> In-Reply-To: <20040819065155.GR85432@wantadilla.lemis.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, hits=0.0 required=3.8 tests=none autolearn=no version=2.63 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on pooker.samsco.org cc: John-Mark Gurney cc: src-committers@FreeBSD.org cc: Pawel Jakub Dawidek cc: cvs-src@FreeBSD.org cc: cvs-all@FreeBSD.org cc: Poul-Henning Kamp cc: Wilko Bulte Subject: Re: RAID-3? X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 Aug 2004 06:59:06 -0000 Greg 'groggy' Lehey wrote: > On Wednesday, 18 August 2004 at 23:44:01 -0700, John-Mark Gurney wrote: > >>I originaly was working on a RAID-3 module (which is possibly where >>pjd got his idea) that used Luigi's FEC code. The advantage of this >>code was the fact that you could have n parity disks beyond the m >>data disks. The advantage of this was that you could loose any n >>disks, and your data is still recoverable. Unlike with RAID-4/5 >>implementations where if you happen to loose a second disk (due to a >>power surge or something) while rebuilding, you'd be SOL. That type >>of redundancy is good thing to have. > > > I can see that as a great advantage, but it's not part of the RAID-3 > definition, and I can't see why you couldn't expand RAID-5 in a > similar manner. Am I missing something? > > Greg Yes, you are! The advantage of RAID-3 is that there are NO Read-Modify-Write cycles when writing blocks. Period. Zippo. None. Every write takes exactly the same amount of time. There is no waiting for data to be read off of any disks. That is why it's nice to applications that require fixed latency. RAID-3 has no concept of stripe sizes becuase of this, unlike 4 and 5. Scott