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Date: Thu, 27 Aug 2009 12:54:05 -0400 From: Jeff Garzik <jeff@...zik.org> To: Ric Wheeler <rwheeler@...hat.com> CC: Theodore Tso <tytso@....edu>, Rob Landley <rob@...dley.net>, Pavel Machek <pavel@....cz>, Florian Weimer <fweimer@....de>, Goswin von Brederlow <goswin-v-b@....de>, kernel list <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...l.org>, mtk.manpages@...il.com, rdunlap@...otime.net, linux-doc@...r.kernel.org, linux-ext4@...r.kernel.org, corbet@....net Subject: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible) 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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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