From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Wed, 01 Oct 2008 13:37:43 -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 m91KbcjK007312 for ; Wed, 1 Oct 2008 13:37:40 -0700 Received: from one.firstfloor.org (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id EE333134E1F8 for ; Wed, 1 Oct 2008 13:39:15 -0700 (PDT) Received: from one.firstfloor.org (one.firstfloor.org [213.235.205.2]) by cuda.sgi.com with ESMTP id O3szKCEBOFU5haKA for ; Wed, 01 Oct 2008 13:39:15 -0700 (PDT) Date: Wed, 1 Oct 2008 22:44:50 +0200 From: Andi Kleen Subject: Re: RAID5/6 writes Message-ID: <20081001204450.GA25711@one.firstfloor.org> References: <20081001175237.GJ32037@cordes.ca> <87k5csp0pe.fsf@basil.nowhere.org> <20081001201331.GL32037@cordes.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081001201331.GL32037@cordes.ca> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Peter Cordes Cc: Andi Kleen , xfs@oss.sgi.com On Wed, Oct 01, 2008 at 05:13:31PM -0300, Peter Cordes wrote: > On Wed, Oct 01, 2008 at 09:36:13PM +0200, Andi Kleen wrote: > > Peter Cordes writes: > > > > > > XFS knows (or should have been told by the admin with mkfs!) what the > > > stripe geometry is: block size and stripe width. So it could apply > > > this optimization only if it would make a write cover more whole > > > blocks or whole stripes. > > > > It's a nice idea, but I don't think XFS knows the actual RAID level, > > only the stripes. And for 0/1 it wouldn't be a good idea. > > Yeah, this would have to be a mount option, like stripewrite=1. > There are already a few other essential mount options people need to > learn about for big RAIDs, e.g. inode64. The other problem I can think of is that determing if something is free data might need more read IO if the free extent tree is not completely cached. -Andi