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Date: Thu, 27 Aug 2009 19:09:42 +0100
From: Alasdair G Kergon <agk@redhat.com>
To: Jeff Garzik <jeff@garzik.org>
Cc: Ric Wheeler <rwheeler@redhat.com>, Theodore Tso <tytso@mit.edu>,
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Subject: Re: MD/DM and barriers (was Re: [patch] ext2/3: document
	conditions when reliable operation is possible)
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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