From owner-freebsd-stable@FreeBSD.ORG Tue Apr 1 06:26:14 2003 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id EEE8837B404 for ; Tue, 1 Apr 2003 06:26:14 -0800 (PST) Received: from smtpproxy1.mitre.org (smtpproxy1.mitre.org [192.160.51.75]) by mx1.FreeBSD.org (Postfix) with ESMTP id B639843F93 for ; Tue, 1 Apr 2003 06:26:13 -0800 (PST) (envelope-from jandrese@mitre.org) Received: from avsrv1.mitre.org (avsrv1.mitre.org [129.83.20.58]) by smtpproxy1.mitre.org (8.12.9/8.12.8) with ESMTP id h31EQDJS001911; Tue, 1 Apr 2003 09:26:13 -0500 (EST) Received: from MAILHUB1 (mailhub1.mitre.org [129.83.20.31]) by smtpsrv1.mitre.org (8.12.9/8.12.8) with ESMTP id h31EQBCg026650; Tue, 1 Apr 2003 09:26:11 -0500 (EST) Received: from mm112324-2k.mitre.org (128.29.3.65) by mailhub1.mitre.org with SMTP id 1741469; Tue, 01 Apr 2003 09:26:05 -0500 Message-ID: <3E89A17C.6030003@mitre.org> Date: Tue, 01 Apr 2003 09:26:04 -0500 From: Jason Andresen User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.3) Gecko/20030312 X-Accept-Language: en-us, en MIME-Version: 1.0 To: "Michael C. Brenner" References: <3E88AECD.10607@liwing.de> <20030330125138.K23911@leelou.in.tern> <3E870CC7.5000204@mac.com> <20030330175605.E23911@leelou.in.tern> <3E87204C.5060304@ludd.luth.se> <3E88524A.1060600@mitre.org> <3E88AECD.10607@liwing.de> <5.2.0.9.2.20030331214429.02677a90@gw.kaibren.com> In-Reply-To: <5.2.0.9.2.20030331214429.02677a90@gw.kaibren.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit cc: FreeBSD Stable List Subject: Re: vinum performance X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 01 Apr 2003 14:26:15 -0000 Michael C. Brenner wrote: > Writing to a RAID5 stripe set requires that all disks in the array > successfully report completion before the RAID5 controller's buffer can > be released back to the cache. (Applies to either software or hardware > raid.) If you are doing a large block write (like dd) you can easily > fill the cache on most controllers. Once the cache is full, the > controller slows each write to the LONGEST completion time of each > spindle in the array. ECC calculation becomes part of the latency also. > In a 5 drive system (other than one where the cache is larger than the > largest file being written as in a large EMC array) the writes are > always about 4-5 times longer than the reads. Tuning stripes and > blocking factors can speed up a specific transfer but RAID5 has always > been slow to write large data and best for read mostly data. Ahh, that makes sesnse. > Read operations benefit from RAID5 or mirrors. Now the shortest > completion time of the minimal drive set is the gating event. The first > set of drives to deliver the data block ends the operation. This makes a > 2 to 1 difference into a 4 to one difference. Thanks for clearing this up. -- \ |_ _|__ __|_ \ __| Jason Andresen jandrese@mitre.org |\/ | | | / _| Network and Distributed Systems Engineer _| _|___| _| _|_\___| Office: 703-883-7755