Please use the PVE Storage Manger tool 'pvesm'.
To list all volumes used by a vm do (for VM 101):
# pvesm list --vmid 101
store2:vm-101-disk-1 101 raw 2097152
And if you want to know the physical path of that volume use:
# pvesm path store2:vm-101-disk-1
/dev/testtest2/vm-101-disk-1
- Dietmar