From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755078AbZEXBv4 (ORCPT ); Sat, 23 May 2009 21:51:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753876AbZEXBvs (ORCPT ); Sat, 23 May 2009 21:51:48 -0400 Received: from cantor2.suse.de ([195.135.220.15]:33546 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753041AbZEXBvs (ORCPT ); Sat, 23 May 2009 21:51:48 -0400 From: "NeilBrown" To: "Ken Milmore" Date: Sun, 24 May 2009 11:51:37 +1000 (EST) Message-ID: <0fa4b1e19d3edb12931e0d641ce2c7d7.squirrel@neil.brown.name> In-Reply-To: <4A188CAD.1080009@googlemail.com> References: <4A188CAD.1080009@googlemail.com> Subject: Re: Write barriers on MD RAID1 Cc: linux-kernel@vger.kernel.org, "Jens Axboe" User-Agent: SquirrelMail/1.4.15 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 24, 2009 9:54 am, Ken Milmore wrote: > > Support for write barriers on MD RAID1 devices appears to be broken on > 2.6.29 and later kernels. Mounting an ext3 or ext4 filesystem over an > md raid1 block device gives the kernel message: > > JBD: barrier-based sync failed on md0 - disabling barriers > > Is this intentional? It looks like a regression to me, since write > barriers (ostensibly) worked for MD RAID1 on earlier kernels (well, all > of the 2.6.27 series at least...) > > Doing a git bisect suggested that this is the culprit: > > commit cec0707e40ae25794b5a2de7b7f03c51961f80d9 > Author: Jens Axboe > Date: Tue Jan 13 15:28:32 2009 +0100 > > block: silently error an unsupported barrier bio Yes, that patch is broken. the new code it introduces should probably go in the top of __make_request rather than just before the call to ->make_request_fn. make_request_fn functions other than __make_request generally don't use ->next_ordered at all. Jens? Would you agree? NeilBrown > > Rolling this back from 2.6.29.4 made the JBD error message go away for > me. I tried to do some disk benchmarking to determine if write barriers > were really still working, but the results were not very conclusive. > > Details of test setup: > - 2.6.29.4 kernel (config from slackware-current) > - ext3 filesystem (mounted with barrier=1), also tried ext4 > - MD RAID1 block device over two SATA disks > - Intel motherboard AHCI controller (82801) > > I got similar behaviour on a virtualised setup using qemu, with the RAID > over two emulated IDE disks. > > Please contact me if I can provide any further information. > > -Ken Milmore. >