From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ric Wheeler Subject: Fwd: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible) Date: Thu, 27 Aug 2009 13:13:18 -0400 Message-ID: <4A96BEAE.5000504@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development List-Id: dm-devel.ids fyi - end of a very long thread, but I thought that dm had this fixed... ric -------- Original Message -------- 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 From: Jeff Garzik To: Ric Wheeler 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 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