From owner-freebsd-performance@FreeBSD.ORG Mon May 2 13:25:32 2005 Return-Path: Delivered-To: freebsd-performance@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id BAF7916A4CE; Mon, 2 May 2005 13:25:32 +0000 (GMT) Received: from multiplay.co.uk (www1.multiplay.co.uk [212.42.16.7]) by mx1.FreeBSD.org (Postfix) with ESMTP id F008143D49; Mon, 2 May 2005 13:25:31 +0000 (GMT) (envelope-from killing@multiplay.co.uk) Received: from vader ([212.135.219.179]) by multiplay.co.uk (multiplay.co.uk [212.42.16.7]) (MDaemon.PRO.v8.0.1.R) with ESMTP id md50001375517.msg; Mon, 02 May 2005 14:21:36 +0100 Message-ID: <002201c54f1a$5c05dfc0$b3db87d4@multiplay.co.uk> From: "Steven Hartland" To: "Eric Anderson" , "Poul-Henning Kamp" References: <17442.1115039706@critter.freebsd.dk> Date: Mon, 2 May 2005 14:25:04 +0100 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2527 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2527 X-Spam-Processed: multiplay.co.uk, Mon, 02 May 2005 14:21:36 +0100 (not processed: message from valid local sender) X-MDRemoteIP: 212.135.219.179 X-Return-Path: killing@multiplay.co.uk X-MDAV-Processed: multiplay.co.uk, Mon, 02 May 2005 14:21:37 +0100 cc: freebsd-performance@freebsd.org cc: Robert Watson cc: =?iso-8859-1?Q?=22Arne_\=22W=F6rner\=22=22?= Subject: Re: Very low disk performance on 5.x X-BeenThere: freebsd-performance@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Performance/tuning List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 May 2005 13:25:32 -0000 ----- Original Message ----- From: "Poul-Henning Kamp" >>Don't mean to be terse here, but I'm talking about the same test done an >>two different RAID5 configurations, with different disks, and not just >>me - other users in this very thread see the same issue.. > > Uhm, if you are using RAID5 and your requests are not aligned and > sized after the RAID5 you should *expect* read performance to be poor. > > If you your request ends up accessing two different blocks even just > once per stripe, this totally kills performance. Interesting stuff so: 1. How to we test if this is happening? 2. How do we prevent it from happening? 3. Why would this be effecting reads and not writes as surely the same blocking is being done for both? RAID5 is becoming more and more the norm with disk and controller prices dropping and as such I think it would be good if could get this. one sorted. Steve ================================================ This e.mail is private and confidential between Multiplay (UK) Ltd. and the person or entity to whom it is addressed. In the event of misdirection, the recipient is prohibited from using, copying, printing or otherwise disseminating it or any information contained in it. In the event of misdirection, illegible or incomplete transmission please telephone (023) 8024 3137 or return the E.mail to postmaster@multiplay.co.uk.