From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Sat, 01 Nov 2008 05:14:57 -0700 (PDT) Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id mA1CEibX007056 for ; Sat, 1 Nov 2008 05:14:44 -0700 Received: from hole.yuiop.co.uk (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id D90131B71EB8 for ; Sat, 1 Nov 2008 05:14:45 -0700 (PDT) Received: from hole.yuiop.co.uk (hole.yuiop.co.uk [89.145.97.62]) by cuda.sgi.com with ESMTP id sZAt6uBWmkezPo4Q for ; Sat, 01 Nov 2008 05:14:45 -0700 (PDT) Message-ID: <490C4834.3050404@anonymous.org.uk> Date: Sat, 01 Nov 2008 12:14:44 +0000 From: John Robinson MIME-Version: 1.0 Subject: Re: Linux RAID & XFS Question - Multiple levels of concurrency = faster I/O on md/RAID 5? References: <490C359F.7080504@anonymous.org.uk> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Justin Piszcz Cc: linux-raid@vger.kernel.org, xfs@oss.sgi.com On 01/11/2008 12:00, Justin Piszcz wrote: > On Sat, 1 Nov 2008, John Robinson wrote: >> On 01/11/2008 08:29, Justin Piszcz wrote: >> [...] >>> Why is running 3 jobs con-currently that take care of two parts each >>> more than >>> twice as fast than running one job for six parts? >> >> Because you have multiple CPUs? > > So 1/4 of a quad core q6600 cannot achieve higher rates of I/O due to the > parity operations being that costly? > > Is the only way to increase the single-threaded speed to increase the > maximum > CPU core speed/get a faster CPU, and/or theoretically a multi-threaded > md-raid > could maximize throughput? Actually I was thinking that your test job - I think you said it used tar - is single-threaded and CPU-bound on one core, and doesn't saturate the MD subsystem. Your jobs are 75% user time to 25% system time, and the user time is not parellelisable until you do it yourself by splitting the work up. Cheers, John.