HP StorageWorks 2000 Series Reference Manual page 263

The high-availability configuration requires two gigabit Ethernet (GbE) switches.
During active-active operation, both controllers' mapped volumes are visible to both
data hosts.
A dual-controller MSA2012i storage system uses port 0 of each controller as one
failover pair and port 1 of each controller as a second failover pair. If one controller
fails, all mapped volumes remain visible to all hosts. Dual IP-address technology is
used in the failed-over state, and is largely transparent to the host system.The
following figure shows how port IP addresses and mapped volumes are presented
when both controllers are active.