[dm-crypt] Does dm-crypt support journaling filesystem transactional guarantees?
yanghatespam at gmail.com
Tue Apr 24 10:16:45 CEST 2012
On Tue, Apr 24, 2012 at 1:14 AM, Arno Wagner <arno at 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
>> > 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
>> You can also use blktrace to see how are fs requests propagated
>> to physical media.
>> dm-crypt mailing list
>> dm-crypt at saout.de
> Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno at wagner.name
> GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
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> with doubt and indecision. -- Bertrand Russell
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