From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Sun, 25 Mar 2007 17:01:14 -0700 (PDT) Received: from mx1.suse.de (mail.suse.de [195.135.220.2]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id l2Q0196p006266 for ; Sun, 25 Mar 2007 17:01:10 -0700 From: Neil Brown Date: Mon, 26 Mar 2007 10:01:01 +1000 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <17927.3389.655835.610940@notabene.brown> Subject: Re: XFS and write barriers. In-Reply-To: message from David Chinner on Sunday March 25 References: <17923.11463.459927.628762@notabene.brown> <1755676AA526FF7790546385@timothy-shimmins-power-mac-g5.local> <17923.35118.139991.252734@notabene.brown> <20070325031927.GG32602149@melbourne.sgi.com> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: David Chinner Cc: Neil Brown , Timothy Shimmin , xfs@oss.sgi.com On Sunday March 25, dgc@sgi.com wrote: > On Fri, Mar 23, 2007 at 07:00:46PM +1100, Neil Brown wrote: > > > > Why no barriers on an external log device??? Not important, just > > curious. > > because we need to synchronize across 2 devices, not one, so issuing > barriers on an external log device does nothing to order the metadata > written to the other device... Right, of course. Just like over a raid0. So you must have code to wait for all writes to the main device before writing the commit block on the journal. How hard is it to fall-back to that if the barrier fails? NeilBrown