From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262386AbTLPU7E (ORCPT ); Tue, 16 Dec 2003 15:59:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262427AbTLPU7E (ORCPT ); Tue, 16 Dec 2003 15:59:04 -0500 Received: from mtaw4.prodigy.net ([64.164.98.52]:21980 "EHLO mtaw4.prodigy.net") by vger.kernel.org with ESMTP id S262386AbTLPU7B (ORCPT ); Tue, 16 Dec 2003 15:59:01 -0500 Date: Tue, 16 Dec 2003 12:58:53 -0800 From: Mike Fedyk To: Linus Torvalds Cc: Helge Hafting , jw schultz , Linux Kernel Mailing List Subject: Re: raid0 slower than devices it is assembled of? Message-ID: <20031216205853.GC1402@matchmail.com> Mail-Followup-To: Linus Torvalds , Helge Hafting , jw schultz , Linux Kernel Mailing List References: <200312151434.54886.adasi@kernel.pl> <20031216040156.GJ12726@pegasys.ws> <3FDF1C03.2020509@aitel.hist.no> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 16, 2003 at 08:42:52AM -0800, Linus Torvalds wrote: > My personal guess is that modern RAID0 stripes should be on the order of > several MEGABYTES in size rather than the few hundred kB that most people > use (not to mention the people who have 32kB stripes or smaller - they > just kill their IO access patterns with that, and put the CPU at > ridiculous strain). Larger stripes may help in general, but I'd suggest that for raid5 (ie, not raid0), the stripe size should not be enlarged as much. On many filesystems, a bitmap change, or inode table update shouldn't require reading a large stripe from several drives to complete the pairity calculations. Probably finding the largest block of data the drive can return in one command would be a good size for a raid5 stripe. That's just speculation though.