allows you to backup the metadata
of your volume groups.
If you don't name any volume groups on the command line, all of them
will be backed up.
In a default installation, each volume group gets backed up into a separate
file bearing the name of the volume group in the directory /etc/lvm/backup.
You can write the backup to an alternative file using -f. In this case
if you are backing up more than one volume group the filename is
treated as a template, and %s gets replaced by the volume group name.
NB. This DOESN'T backup user/system data in logical
volume(s)! Backup /etc/lvm regularly too.