Howtoforge published a guide about backup and restore LVM Partitions with LVM snapshots

This tutorial shows how you can create backups of LVM partitions with an LVM feature called LVM snapshots. An LVM snapshot is an exact copy of an LVM partition that has all the data from the LVM volume from the time the snapshot was created. The big advantage of LVM snapshots is that you do not have to worry about open files and database connections, and you do not have to interrupt/halt services on the live partition because a snapshot is usually created in fractions of a second, so your users will not notice any disruption, and your snapshot holds consistent data.

Back Up (And Restore) LVM Partitions With LVM Snapshots