From owner-freebsd-questions@FreeBSD.ORG Wed Mar 3 14:47:18 2004 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id A3A9516A4CE for ; Wed, 3 Mar 2004 14:47:18 -0800 (PST) Received: from smtpout.mac.com (A17-250-248-83.apple.com [17.250.248.83]) by mx1.FreeBSD.org (Postfix) with ESMTP id 960FB43D3F for ; Wed, 3 Mar 2004 14:47:18 -0800 (PST) (envelope-from cswiger@mac.com) Received: from mac.com (smtpin07-en2 [10.13.10.152]) by smtpout.mac.com (8.12.6/MantshX 2.0) with ESMTP id i23Mlaw7011149; Wed, 3 Mar 2004 14:47:38 -0800 (PST) Received: from [10.1.1.193] ([199.103.21.225]) (authenticated bits=0) by mac.com (Xserve/smtpin07/MantshX 3.0) with ESMTP id i23MlEgv007458; Wed, 3 Mar 2004 14:47:15 -0800 (PST) In-Reply-To: <000601c4016d$cdb571e0$0a06a8c0@rekon> References: <000601c4016d$cdb571e0$0a06a8c0@rekon> Mime-Version: 1.0 (Apple Message framework v612) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: Content-Transfer-Encoding: 7bit From: Charles Swiger Date: Wed, 3 Mar 2004 17:47:29 -0500 To: Reko Turja X-Mailer: Apple Mail (2.612) cc: 'Free BSD Questions list' Subject: Re: 1 processor vs. 2 X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 03 Mar 2004 22:47:18 -0000 On Mar 3, 2004, at 5:20 PM, Reko Turja wrote: >> RAID-1 will be about 50% faster than RAID-5 doing reads regardless of >> size, and will also be *much* faster doing small writes-- by a factor >> of 4, perhaps. > > The abovementioned figures seem more like comparing RAID-0 (striping) > to RAID-5 (striping with ECC) than RAID-5 to RAID-1 (mirroring). In > my experience mirroring is always the slowest RAID in terms of > retrieving data, writes might be quite comparable with RAID-1 and > RAID-5 though. Your mileage may vary. :-) However, consider that RAID-1 (mirroring) read performance should always be better than RAID-0 (striping) because you can get the data you want using a single read from either device regardless of size, and you can do things like distribute reads geometrically to reduce head motion for the RAID-1 case-- whereas with reads above the stripe size, the RAID-0 case requires you to access both devices and glue the results together. -- -Chuck