[Duplicity-talk] Direct backup of LVM snapshot partitions?

[George MacKerron]

Hi all.

I'm trying to use duplicity to back up LVM snapshots (which are Xen domU 
disks). 

I've seen scripts that take a snapshot, mount the snapshot, and then back up 
the files inside it. But my preference is to just back up the LVM logical 
volume directly. I feel more comfortable knowing I have an exact, 
filesystem-level snapshot.

However, this doesn't appear to work: if I specify a volume such as /dev/dm-10, 
this isn't backed up. So at the moment I am using dd to copy the volume data to 
a temporary file, and then using Duplicity on this. However, this causes a lot 
of seemingly unnecessary disk thrashing.

So, a couple of questions:

1. Should Duplicity be able to back up the LVM partition directly? If so, how? 
(If not, why?).

2. Am I misguided? Is it a much better idea just to mount the snapshot and back 
up the files? If so, why?

Many thanks,
George