undo LVM

[Luis Paulo]

On Mon, May 17, 2010 at 11:49 AM, Dave Howorth
<dhoworth at mrc-lmb.cam.ac.uk> wrote:
> Michel Racic wrote:
>> Hi Luis
>>
>> Yes I know how important backups are and I gave most of my urgent data
>> backed up on various places but this 1TB disc is my main backup and My
>> other disc crashed...
>>
>> I'm too pussy to just try that out so I first have to get a new 1TB disc
>> and dd (mirror) the disc so I can try this out on the mirror disc...
>>
>> I don't think that vgreduce will work but i try as soon I have the
>> mirror disc
>
> I don't have a solution I'm afraid but here's my understanding:
> (1) you've created a PV and VG but not an LV
> (2) the result of (1) is that you have some LVM metadata written in
> partition /dev/sdb1
> (3) you need to replace that LVM metadata with whatever LUKS data was
> there before
> (4) AFAIK, LVM does not keep a copy of what was on the disk before it
> writes its metadata (not unreasonable, neither do any other format
> operations!)
> (5) So there's no way that any LVM operation could help you. The best
> effect that running any more LVM commands can have is nothing; the worst
> case is further damage
> (6) So AIUI, your only hope of recovering data is if LUKS keeps backups
> of that area of the disk for some reason, or if it has some kind of
> error recovery, or if the data layout is localised so you only lose a
> few blocks (I know nothing at all about it)
>
> i.e IMHO your question is really about how to recover lost LUKS data
> blocks and nothing to do with LVM. Probably not what you want to hear,
> sorry. :(
>
> Dave

Hi, Dave

You made a good point, I agree.

I was thinking that luks was a file encryption software, now I saw it
encrypts a partition (As I said, I know nothing about luks or
encryption)

But, from luks page
(http://www.saout.de/tikiwiki/tiki-index.php?page=EncryptedDeviceUsingLUKS):

To mount:
# cryptsetup luksOpen /dev/sdc1 sdc1
Enter LUKS passphrase: (enter passphrase)
key slot 0 unlocked.
# mount /dev/mapper/sdc1 /home4

As far as I understood, from what was said, there is no reason to
think lvm has messed any of the luks information

t is possible, maybe probable. But with Michel strategy of doing a
disk clone, trying to remove lvm info, mount the encrypted partition
as it was mounted before, and try if luks will read it, it's worth
trying.

I would. Right? :)
If that fails, then I would follow your line of thinking. That because
I think vgreduce and lvremove will not produce more damage. And if so,
it will be on the cloned disk, which was good thinking from Michel,
must add.

Regards
Luis