From owner-freebsd-questions@FreeBSD.ORG Sat Jan 24 10:03:39 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 EDB8E16A4CE for ; Sat, 24 Jan 2004 10:03:39 -0800 (PST) Received: from smtpout.mac.com (smtpout.mac.com [17.250.248.44]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9FF2B43D53 for ; Sat, 24 Jan 2004 10:03:37 -0800 (PST) (envelope-from cswiger@mac.com) Received: from mac.com (smtpin07-en2 [10.13.10.152]) by smtpout.mac.com (Xserve/MantshX 2.0) with ESMTP id i0OI3Xf0011124; Sat, 24 Jan 2004 10:03:34 -0800 (PST) Received: from [192.168.1.6] (pool-68-161-129-47.ny325.east.verizon.net [68.161.129.47]) (authenticated bits=0)i0OI3XeO016621; Sat, 24 Jan 2004 10:03:33 -0800 (PST) In-Reply-To: <401207EF.7030005@cal.berkeley.edu> References: <401207EF.7030005@cal.berkeley.edu> Mime-Version: 1.0 (Apple Message framework v609) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: Content-Transfer-Encoding: 7bit From: Charles Swiger Date: Sat, 24 Jan 2004 13:03:39 -0500 To: Rishi Chopra X-Mailer: Apple Mail (2.609) 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: Sat, 24 Jan 2004 18:03:40 -0000 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. -- -Chuck