How do I manage SAN based snapshots of LVM volumes?
Some people prefer to use their SAN's built in snapshot capabilities instead of LVM's snapshot capabilities. Creating snapshots of a LVM volume on a SAN then presenting the snapshot back to the same server that the snapshot was taken from doesn't work as some people expect. When this is done you encounter "Found duplicate PV" messages and won't be able to activate the Volume Group (how would you anyway, its got the same name and UUID as its origin/parent).
Each LVM Physical Volume (PV), Volume Group (VG) and Logical Volume (LV) has a UUID - they're used for identification by LVM. When you create a snapshot of server X's LVM volume on the SAN then present the new snapshot back to the same server (X) the UUIDs of the original volume (the snapshot origin) will match the UUID in the new snapshot (it is a snapshot after all!) Since the volume is basically a clone, the UUID in the LVM metadata is the same as its origin/parent and therefore its not unique, hence the "Found duplicate PV" message.
It is possible to use SAN based snapshots on a system that uses LVM. Instructions for doing so can be found here.