From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964814AbWGPAE7 (ORCPT ); Sat, 15 Jul 2006 20:04:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964815AbWGPAE7 (ORCPT ); Sat, 15 Jul 2006 20:04:59 -0400 Received: from wr-out-0506.google.com ([64.233.184.236]:12462 "EHLO wr-out-0506.google.com") by vger.kernel.org with ESMTP id S964814AbWGPAE6 (ORCPT ); Sat, 15 Jul 2006 20:04:58 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:mime-version:content-type:content-transfer-encoding:content-disposition; b=uaEA1KOS94sR7/Yy50n7Wm3U3nHPf10OE9T0+vVM7GxlluBoq9mM38YI9hp6m8EjGtmZWdDW1ix3SGUjqLiGPlBLym4D0VQofFAmCig7zxDosC72qd+XV7W1QUyfx2oANs6i63K1XuZAbArEaCRoUJ8fisJxtpK/w3sKTinF1cI= Message-ID: Date: Sat, 15 Jul 2006 17:04:57 -0700 From: "Jonathan Baccash" To: linux-kernel@vger.kernel.org Subject: raid io requests not parallel? MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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 MT Random read: 5.276 sec MT Random write: 19.839 sec As expected, the multi-threaded reads are 2x as fast as single-threaded reads. But I would have expected (assuming the write to both disks can occur in parallel) that the random writes are about the same speed (10 seconds) as the single-threaded random reads, for both the single-threaded and multi-threaded write cases. The fact that the multi-threaded reads were twice as fast indicates to me that read requests can occur in parallel. So.... why doesn't the raid issue the writes in parallel? Thanks in advance for any help. Jon.