I want advise that there's a small bug in LVM tools on xbmcbunutu 12.
This bugs is derived from ubuntu and it's not critical but it prevents to export the LVM settings.
In particular, the command
vgchange -an volumeGroup
doesn't works and it doesn't deactive the volume group
to deactive the group use :
dmsetup remove /dev/dm-X
I think this is a important information to know when someone will update the XbmxBuntu 13.
Without this stupid workaround it's impossible to remove safely the LVM and install in a new os version.