[dm-devel] Re: [Bug 14354] Status of barrier requests in LVM and dm-crypt?
Mike Snitzer
snitzer at redhat.com
Tue Oct 13 14:49:45 UTC 2009
On Mon, Oct 12 2009 at 2:15pm -0400,
Theodore Ts'o <tytso at mit.edu> wrote:
> Hi, I'm trying to track down a problem relating to ext4 problems, in
> kernel bugzilla 14354. Originally it was thought this was a regression
> 2.6.31->2.6.32-rc1 regression, but the Aneesh Kumar's report shows a
> very similar fsck transcript using a 2.6.30-1 kernel (which makes makes
> it unclear whether this is really a regression or not), and all three
> reports are tied together by the use of device-mapper.
>
> The fsck logs are consistent barriers being disabled. As I recall under
> some circumstances device mapper silently drops barrier requests --- I
> thought this was fixed for device mapper in some cases. What's the
> current status of barrier requests in device mapper? Are they
> faithfully passed for standard (non-RAID) LVM2 volumes? When was this
> changed? What about dm-crypto volumes? (One of the reports was with a
> dm-crypt volume from what I can tell.)
Barrier infrastructure started to get added to the DM core in 2.6.30, see:
http://git.kernel.org/linus/af7e466a1ace
But barriers were not enabled for all DM targets (_except_ dm-multipath)
until 2.6.31. So 2.6.31's dm-crypt does support barriers, see:
http://git.kernel.org/linus/647c7db14ef9
If the underlying device(s) support barriers DM should faithfully pass
them on (again except for dm-multipath). Also, requests with barriers
that result in -EOPNOTSUPP are retried without the barrier, see:
http://git.kernel.org/linus/51aa32284958
Mike
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