From: Shapor Naghibzadeh Subject: Re: More testing: 4x parallel 2G writes, sequential reads Date: Wed, 7 Nov 2007 16:14:34 -0800 Message-ID: <20071108001434.GB16884@yzf.shaptech.com> References: <47323F73.5080708@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: ext4 development To: Eric Sandeen Return-path: Received: from yzf.shapor.com ([216.75.12.152]:33766 "EHLO yzf.shapor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755910AbXKHAla (ORCPT ); Wed, 7 Nov 2007 19:41:30 -0500 Content-Disposition: inline In-Reply-To: <47323F73.5080708@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, Nov 07, 2007 at 04:42:59PM -0600, Eric Sandeen wrote: > Again this was on a decent HW raid so seek penalties are probably not > too bad. You may want to verify that by doing a benchmark on the raw device. I recently did some benchmarks doing random I/O on a Dell 2850 w/ a PERC (megaraid) RAID5 w/ 128MB onboard writeback cache and 6x 15krpm drives and noticed appoximately one order of magnitude throughput drop on small (stripe-sized) random reads versus linear. It maxed out at ~100 random read IOPs or "seeks/sec" (suprisingly low). Out of curiousity, how are you counting the seeks? Shapor