From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alasdair G Kergon <agk@redhat.com>
Subject: Re: MD/DM and barriers (was Re: [patch] ext2/3: document
	conditions when reliable operation is possible)
Date: Thu, 27 Aug 2009 19:09:42 +0100
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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> <4A96BA2D.60804@garzik.org>
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Cc: Ric Wheeler <rwheeler@redhat.com>, Theodore Tso <tytso@mit.edu>,
	Rob Landley <rob@landley.net>, Pavel Machek <pavel@ucw.cz>,
	Florian Weimer <fweimer@bfk.de>,
	Goswin von Brederlow <goswin-v-b@web.de>,
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	rdunlap@xenotime.net, linux-doc@vger.kernel.org,
	linux-ext4@vger.kernel.org, corbet@lwn.net,
	Mikulas Patocka <mpatocka@redhat.com>
To: Jeff Garzik <jeff@garzik.org>
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On Thu, Aug 27, 2009 at 12:54:05PM -0400, Jeff Garzik wrote:
> 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.

That code is from the new request-based multipath implementation in 2.6.31
which doesn't yet.

But bio-based dm does support barriers now.  (Just missing some patches to
complete the dm-raid1 support that are still under review IIRC.)

Alasdair