From owner-freebsd-questions@FreeBSD.ORG Sat Jan 24 19:49:38 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 8034916A4CE for ; Sat, 24 Jan 2004 19:49:38 -0800 (PST) Received: from m00.ca.astound.net (m00.ca.astound.net [64.85.239.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8C5C543D2F for ; Sat, 24 Jan 2004 19:49:34 -0800 (PST) (envelope-from rchopra@cal.berkeley.edu) Received: from cal.berkeley.edu (astound-64-85-244-72.ca.astound.net [64.85.244.72]) by m00.ca.astound.net (8.12.10/8.12.10) with ESMTP id i0P3mJKL004410; Sat, 24 Jan 2004 19:48:19 -0800 Message-ID: <40133C7F.2090803@cal.berkeley.edu> Date: Sat, 24 Jan 2004 19:48:15 -0800 From: Rishi Chopra User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.6b) Gecko/20031205 Thunderbird/0.4 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Charles Swiger References: <401207EF.7030005@cal.berkeley.edu> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: by amavisd-new cc: questions@freebsd.org Subject: Re: Adaptec 2400A Performance 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: Sun, 25 Jan 2004 03:49:38 -0000 Just wanted to make sure I wasn't skipping any obvious steps. One other (slightly lamer) question: if my device configures as da0, is that scsi or ide? The reason I ask is I wish to write a custom kernel, and would like to eliminate all unnecessary configurations/devices. Charles Swiger wrote: > On Jan 24, 2004, at 12:51 AM, Rishi Chopra wrote: > >> I was rather disappointed with the results. Can anyone suggest what >> might be causing such slow disk speeds, or whether these speeds are >> out of the ordinary for a 4-disk FreeBSD RAID5 installation? I have >> done nothing to configure the card aside from striping the array in >> BIOS; FreeBSD seems to automatically detect the disks. > > > For us to be able to comment beyond generalizations, it's necessary to > also benchmark how a single disk performs. I can still answer your > question, though: > > RAID-5 is slow. RAID-5 trades availability against performance and > hardware costs. With RAID-0, n drives gives n drives' worth of usable > space. With RAID-5, n drives gives n-1 drives' worth of usable space. > The performance is between RAID-0 and RAID-1 is comparible for large > accesses. For small accesses, particularly small writes, RAID-5 > performance is much worse than plain RAID-0 or a plain disk. > -- Rishi Chopra http://www.ocf.berkeley.edu/~rchopra