How can I prove two or more multipathed devices are in one path group when using dm-multipath?

DM-Multipath can provide failover in an active/passive configuration. In an active/passive configuration, only half the paths are used at any time for I/O. If any element of an I/O path (the cable, switch, or controller) fails, DM-Multipath switches to an alternate path. DM-Multipath can be configured in active/active mode, where I/O is spread over the paths in a round-robin fashion. In some c...