It may already be activated, where “activated” just means that the kernel is aware of the LVM.
Run lvscan and see if it is on the list. If not, then it needs to be activated before it can be accessed.
Regarding LVM maintenance, there is a good HowTo here http://www.ibiblio.org/pub/Linux/doc...LVM-HOWTO.html
Chapter 11. “Common Tasks” is especially useful.
For more details about the commands, see: