From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751191AbWGQAVO (ORCPT ); Sun, 16 Jul 2006 20:21:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751343AbWGQAVO (ORCPT ); Sun, 16 Jul 2006 20:21:14 -0400 Received: from [216.208.38.107] ([216.208.38.107]:24710 "EHLO OTTLS.pngxnet.com") by vger.kernel.org with ESMTP id S1751191AbWGQAVN (ORCPT ); Sun, 16 Jul 2006 20:21:13 -0400 Date: Mon, 17 Jul 2006 02:20:07 +0200 From: Jens Axboe To: Neil Brown Cc: Jonathan Baccash , linux-kernel@vger.kernel.org Subject: Re: raid io requests not parallel? Message-ID: <20060717002007.GA5032@suse.de> References: <17594.53980.497790.409035@cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <17594.53980.497790.409035@cse.unsw.edu.au> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 17 2006, Neil Brown wrote: > On Saturday July 15, jbaccash@gmail.com wrote: > > I'm using kernel linux-2.6.15-gentoo-r1, and I noticed performance of > > the software RAID-1 is not as good as I would have expected on my two > > SATA drives, and I was wondering if anyone has an idea what may be > > happening. The test I run is 1024 16k direct-IO reads/writes from > > random locations within a 1GB file (on a RAID-1 partition), with my > > disk caches set to > > write-through mode. In the MT (multi-threaded) case, I issue them from > > 8 threads (so it's 128 requests per thread): > > > > Random read: 10.295 sec > > Random write: 19.142 sec > > Odd. I would expect these two numbers to be a lot closer together. > > Try changing the IO scheduler on the drives and see if it makes a > difference. > e.g. > cat /sys/block/XXX/queue/scheduler > echo cfq > /sys/block/XXX/queue/scheduler > echo deadline > /sys/block/XXX/queue/scheduler > > See what works best. His cache is set to write through, 16kb direct writes in that case will be a lot slower than the equivalent reads. 10 vs 20 seconds does not sounds out of the question. -- Jens Axboe