[dm-crypt] Open raid1 with luks encryption after a raid re-create

Arno Wagner arno at wagner.name
Mon Nov 23 07:26:27 CET 2015

On Mon, Nov 23, 2015 at 04:56:34 CET, Sven Eschenberg wrote:
> Am 23.11.2015 um 04:35 schrieb Arno Wagner:
> >On Sun, Nov 22, 2015 at 23:30:23 CET, Sven Eschenberg wrote:
> >[...]
> >>Now to your question, once you know the offset of the header:
> >>1.)Setup a loop device from your image (You can use an offset into
> >>the image where your loop device starts with sector 0) see --offset
> >>in losetup man page.
> >
> >Ah, yes. That would save copying it.
> That was the plan. In general using dmsetup to create a mapping
> manually should work too, if loop device support is missing -
> dmsetup is pretty cryptic to use though.

"Cryptic" is not good here...

I was not aware that losetup allows read-only mappings, or I 
would probably have looked at it too. 

Excellent! So I learned something too!
> >>Inspect loopdevice if the LUKS Header now is on sector 0
> >>2.)Try a cryptsetup luksopen in readonly mode
> >
> >Good idea. With that it may be reasonaly safe to work
> >with the original disk. I still would make a full
> >backup before.
> >
> >Regards,
> >Arno
> >
> Well, I thought about using the loop on the file while the physical
> disk stays unchanged. Otherwise it would be possible to work on the
> physical disk, and keep a safety image. No matter which way one
> chooses, always have a safety copy.
> If the disk is having mechanical problems or something similiar one
> would of course use 2 images, one 'master binary backup' and the
> replica to work on.
> Once mapping and opening works, one can choose to either copy out
> the files and backup (usually a good idea) or to create a copy in
> the manner you described. Possibly such an image could then be
> remerged onto a new clean array, if it is otherwise intact. Not
> without some remaining risks though.

Indeed. And first things first, lets see whether that header is 
viable before goping any further.

Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
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