From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Wed, 01 Oct 2008 13:12:05 -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 m91KC0P4004910 for ; Wed, 1 Oct 2008 13:12:00 -0700 Received: from smtpout.eastlink.ca (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 0265A134E220 for ; Wed, 1 Oct 2008 13:13:37 -0700 (PDT) Received: from smtpout.eastlink.ca (smtpout.eastlink.ca [24.222.0.30]) by cuda.sgi.com with ESMTP id 6EB6VkjEu037avgb for ; Wed, 01 Oct 2008 13:13:37 -0700 (PDT) Received: from ip02.eastlink.ca ([24.222.39.20]) by mta01.eastlink.ca (Sun Java System Messaging Server 6.2-4.03 (built Sep 22 2005)) with ESMTP id <0K82004T7TIK5031@mta01.eastlink.ca> for xfs@oss.sgi.com; Wed, 01 Oct 2008 17:13:32 -0300 (ADT) Date: Wed, 01 Oct 2008 17:13:31 -0300 From: Peter Cordes Subject: Re: RAID5/6 writes In-reply-to: <87k5csp0pe.fsf@basil.nowhere.org> Message-id: <20081001201331.GL32037@cordes.ca> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7BIT Content-disposition: inline References: <20081001175237.GJ32037@cordes.ca> <87k5csp0pe.fsf@basil.nowhere.org> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Andi Kleen Cc: xfs@oss.sgi.com 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. AFAIK, XFS only knows the stripe geometry (sunit, swidth), not how many parity blocks are part of each stripe, so it can't tell the difference between RAID0 and RAID4,5,6. (let alone RAID60...). XFS on RAID1 will have swidth=0, though. Probably the only sane default is 0, even when swidth!=0, to make sure it doesn't cause problems for anyone or slow down RAID0. Thanks for the CC, since I'm not subscribe to the xfs list. -- #define X(x,y) x##y Peter Cordes ; e-mail: X(peter@cor , des.ca) "The gods confound the man who first found out how to distinguish the hours! Confound him, too, who in this place set up a sundial, to cut and hack my day so wretchedly into small pieces!" -- Plautus, 200 BC