From owner-freebsd-stable@FreeBSD.ORG Mon Mar 31 13:10:41 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 5CAB437B401 for ; Mon, 31 Mar 2003 13:10:41 -0800 (PST) Received: from mail.liwing.de (mail.liwing.de [213.70.188.162]) by mx1.FreeBSD.org (Postfix) with ESMTP id 0069543F3F for ; Mon, 31 Mar 2003 13:10:40 -0800 (PST) (envelope-from rehsack@liwing.de) Received: (qmail 50330 invoked from network); 31 Mar 2003 21:10:38 -0000 Received: from stingray.liwing.de (HELO liwing.de) ([213.70.188.164]) (envelope-sender ) by mail.liwing.de (qmail-ldap-1.03) with SMTP for ; 31 Mar 2003 21:10:38 -0000 Message-ID: <3E88AECD.10607@liwing.de> Date: Mon, 31 Mar 2003 23:10:37 +0200 From: Jens Rehsack Organization: LiWing IT-Services User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jason Andresen References: <20030330125138.K23911@leelou.in.tern> <3E870CC7.5000204@mac.com> <20030330175605.E23911@leelou.in.tern> <3E87204C.5060304@ludd.luth.se> <3E88524A.1060600@mitre.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit cc: freebsd-stable@freebsd.org cc: Lukas Ertl 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: Mon, 31 Mar 2003 21:11:07 -0000 Jason Andresen wrote: > Mattias Pantzare wrote: > >> Lukas Ertl wrote: >> >>> Ok. But I still don't understand why RAID 5 write performance is _so_ >>> bad. >>> The CPU is not the bottle neck, it's rather bored. And I don't >>> understand >>> why RAID 0 doesn't give a big boost at all. Is the ahc driver known >>> to be >>> slow? >> >> >> >> To do a RAID 5 write you do this: >> 1. Read the old data on the blocks that you will write to. >> 2. Read the coresponding parity data. >> 3. Write the new data. >> 4. Write the new parity. > > > Hmm, how about the case where you're writing new data? You shouldn't > have to do steps 1 & 2, and yet the RAID5 write performance is still > abysmial. Remember for that case that a block covered by the raid-system may be larger than 512 bytes. I use 32K for my fileserver, so to skip reading old data I had to write 32K blocks at once. Of course, the system software (either vinum or the controller software) caches a little bit, so if you write enough small data you may get a 32K block (or whatever you use), full. > I get 4565 K/sec on modern ATA/133 HDDs. > > Reading is much better at 91908 K/sec at least. > So long, Jens