Date: Mon, 23 Nov 2015 07:26:27 +0100
From: Arno Wagner <arno@wagner.name>
Message-ID: <20151123062627.GA14309@tansi.org>
References: <loom.20151121T172556-770@post.gmane.org>
 <20151121184914.GA28647@tansi.org> <5651B1CF.7090306@sapo.pt>
 <20151122125233.GA4802@tansi.org> <5651D9B3.6000500@sapo.pt>
 <565241FF.90005@whgl.uni-frankfurt.de>
 <20151123033504.GA12468@tansi.org>
 <56528E72.8090604@whgl.uni-frankfurt.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <56528E72.8090604@whgl.uni-frankfurt.de>
Subject: Re: [dm-crypt] Open raid1 with luks encryption after a raid
	re-create
To: dm-crypt@saout.de

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.

Regards,
Arno
-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
A good decision is based on knowledge and not on numbers. -- Plato

If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier