HP StorageWorks 2000 Series Reference Manual page 258

When a data host is directly connected to controller host ports, loop topology must
be used. The host should have one HBA port connected to each controller.
When the host-port interconnects are enabled, the host has access to both
controllers' mapped volumes.
If one controller fails in this configuration, the interconnects remain active so hosts
can continue to access all mapped volumes without the intervention of host-based
multipathing software. The controllers accomplish this by using FC target multi-ID:
while a controller is failed over, each surviving controller host port presents its own
port WWN and the port WWN of the interconnected, failed controller host port that
was originally connected to the loop. All mapped volumes remain accessible
through the surviving controller until a replacement for the failed controller is
installed.
The following figure shows how port WWNs and mapped volumes are presented
when both controllers are active.