Re: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible)

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To: Jeff Garzik <jeff@xxxxxxxxxx>
Subject: Re: MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible)
From: Alasdair G Kergon <agk@xxxxxxxxxx>
Date: Thu, 27 Aug 2009 19:09:42 +0100
Cc: Ric Wheeler <rwheeler@xxxxxxxxxx>, Theodore Tso <tytso@xxxxxxx>, Rob Landley <rob@xxxxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, Florian Weimer <fweimer@xxxxxx>, Goswin von Brederlow <goswin-v-b@xxxxxx>, kernel list <linux-kernel@xxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxx>, mtk.manpages@xxxxxxxxx, rdunlap@xxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, corbet@xxxxxxx, Mikulas Patocka <mpatocka@xxxxxxxxxx>
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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
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References:
- Re: [patch] ext2/3: document conditions when reliable operation is possible
  - From: Pavel Machek
- Re: [patch] ext2/3: document conditions when reliable operation is possible
  - From: Ric Wheeler
- Re: [patch] ext2/3: document conditions when reliable operation is possible
  - From: Theodore Tso
- Re: [patch] ext2/3: document conditions when reliable operation is possible
  - From: Rob Landley
- Re: [patch] ext2/3: document conditions when reliable operation is possible
  - From: Theodore Tso
- Re: [patch] ext2/3: document conditions when reliable operation is possible
  - From: Ric Wheeler
- MD/DM and barriers (was Re: [patch] ext2/3: document conditions when reliable operation is possible)
  - From: Jeff Garzik

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