* [dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees?
@ 2012-04-24 6:45 Yang Zhang
2012-04-24 7:47 ` Milan Broz
0 siblings, 1 reply; 4+ messages in thread
From: Yang Zhang @ 2012-04-24 6:45 UTC (permalink / raw)
To: dm-crypt
I'm considering using ext4 on encrypted LVM (which uses LUKS and
dm-crypt). Will the transactional guarantees in ext4's journaling be
preserved?
Bonus: where may I find authoritative information on this (besides the source)?
Thanks in advance for any answers.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees?
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
0 siblings, 1 reply; 4+ messages in thread
From: Milan Broz @ 2012-04-24 7:47 UTC (permalink / raw)
To: Yang Zhang; +Cc: dm-crypt
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.)
> 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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees?
2012-04-24 7:47 ` Milan Broz
@ 2012-04-24 8:14 ` Arno Wagner
2012-04-24 8:16 ` Yang Zhang
0 siblings, 1 reply; 4+ messages in thread
From: Arno Wagner @ 2012-04-24 8:14 UTC (permalink / raw)
To: dm-crypt
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees?
2012-04-24 8:14 ` Arno Wagner
@ 2012-04-24 8:16 ` Yang Zhang
0 siblings, 0 replies; 4+ messages in thread
From: Yang Zhang @ 2012-04-24 8:16 UTC (permalink / raw)
To: dm-crypt
On Tue, Apr 24, 2012 at 1:14 AM, Arno Wagner <arno@wagner.name> wrote:
> 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 ;-)
At first I was confused what this was referring to - for posterity,
turns out this is the (very useful) cryptsetup FAQ at
http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions
Thanks!
>
> 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
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt
--
Yang Zhang
http://yz.mit.edu/
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2012-04-24 8:17 UTC | newest]
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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
2012-04-24 8:16 ` Yang Zhang
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