Hello,
when it is a real live environment, than you should mount the storage under Datacenter > Storage > with CIFS (SMB) / NFS and select "VZDump backup file". Under Datacenter > Backup you can configure vzdump tasks for automatical backup.
The pbs is still in beta... At the moment nothing for a real live environment... (But here you can simple mount it with cifs (smb) or nfs.)