From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees?
Date: Tue, 24 Apr 2012 10:14:09 +0200 [thread overview]
Message-ID: <20120424081409.GA17802@tansi.org> (raw)
In-Reply-To: <4F965A9E.7090804@redhat.com>
On Tue, Apr 24, 2012 at 09:47:42AM +0200, Milan Broz wrote:
> On 04/24/2012 08:45 AM, Yang Zhang wrote:
> > I'm considering using ext4 on encrypted LVM (which uses LUKS and
> > dm-crypt). Will the transactional guarantees in ext4's journaling be
> > preserved?
>
> yes. dm-crypt operates in block layer, so it is filesystem responsibility
> to properly set needed bits for IO (flush cache, FUA - force unit access)
> and dmcrypt (device-mapper in general and block layer) must process them.
>
> (read http://lwn.net/Articles/400541/ for more info).
>
> In short, ext4, xfs, btrfs and similar filesystems supports
> all features over dmcrypt.
>
> (Except very old kernels, but most of stable distros backports patches.)
See also FAQ item 2.10, which I just have updated to reflect this
information ;-)
Arno
> > Bonus: where may I find authoritative information on this (besides the source)?
> The source is your best friend :-)
>
> basically this is the first commit introducing real barrier
> (later replaced with FUA) support
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=647c7db14ef9cacc4ccb3683e206b61f0de6dc2b
>
> You can also use blktrace to see how are fs requests propagated
> to physical media.
>
> Milan
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt
>
--
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name
GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
----
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision. -- Bertrand Russell
next prev parent reply other threads:[~2012-04-24 8:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-24 6:45 [dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees? Yang Zhang
2012-04-24 7:47 ` Milan Broz
2012-04-24 8:14 ` Arno Wagner [this message]
2012-04-24 8:16 ` Yang Zhang
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