[dm-devel] Using the dm tools to create a writable "mirror" of a physical disk

[Phillip Susi]

On 02/02/2011 05:31 PM, Anders Andersson wrote:
> Good evening! I was recently given the task of trying to salvage files
> from a 1.5TB harddrive that was accidentally formatted and/or
> repartitioned. Normally I would do a 1:1 copy of the whole drive to a
> file and operate on that, but I simply do not have that much room this
> time.
>
> Ideally I would like to create a writable snapshot in the same way as
> I do with my LVM volumes, storing the changes in a smaller file or in
> another block device so that I can experiment freely without worrying
> about destroying anything else on the drive. Is this possible
> (probably) and easy (probably not?) with any device mapper tools? I'm
> not really sure where I should begin looking, because dmsetup is
> probably pretty low-level.

Yep, you need to use dmsetup.  Documentation/device-mapper/snapshot.txt 
in the kernel sources documents how.