From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible) Date: Thu, 27 Aug 2009 12:54:05 -0400 Message-ID: <4A96BA2D.60804@garzik.org> References: <20090825225114.GE4300@elf.ucw.cz> <4A948C94.7040103@redhat.com> <20090826025849.GF32712@mit.edu> <200908270019.04231.rob@landley.net> <20090827122423.GO6997@mit.edu> <4A9685D4.2070906@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Theodore Tso , Rob Landley , Pavel Machek , Florian Weimer , Goswin von Brederlow , kernel list , Andrew Morton , mtk.manpages@gmail.com, rdunlap@xenotime.net, linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, corbet@lwn.net To: Ric Wheeler Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:41810 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753043AbZH0Qyo (ORCPT ); Thu, 27 Aug 2009 12:54:44 -0400 In-Reply-To: <4A9685D4.2070906@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 08/27/2009 09:10 AM, Ric Wheeler wrote: > One thing that does need fixing for some MD configurations is to stress > again that we need to make sure that barrier operations are properly > supported or users will need to disable the write cache on devices with > volatile write caches. Agreed; chime in on Christoph's linux-vfs thread if people have input. I quickly glanced at MD and DM. Currently, upstream, we see a lot of if (unlikely(bio_barrier(bio))) { bio_endio(bio, -EOPNOTSUPP); return 0; } in DM and MD make_request functions. Only md/raid1 supports barriers at present, it seems. None of the other MD drivers support barriers. DM has some barrier code... but the above code was pasted from DM's make_request function, so I am guessing that DM's barrier stuff is incomplete and disabled at present. I've been mentioning this issue for years... glad some people finally noticed :) Jeff