[linux-lvm] thin snapshot actual usage

[Xen]

Short question.

When a snapshot is created of some thin volume its data_percent is 
typically the same as for its parent volume.

However that doesn't mean it actually uses those extents for itself.

How can I obtain actual information as to how much extents the thin 
volume uses?

I also realized that putting data on a thin volume does not have to 
cause the thin snapshot to allocate more of the previous extents were 
unused?

So for a thin volume that does not see a lot of data *changes* but only 
data *growth* it means all of this data is only allocated once right.

Regards.