Controllers don't fail over on a network outage.   On some array models, the active CM can access the Ethernet port on the passive CM.   This is known as "vertical" fail over.  Even though the CM doesn't actually fail over.   For this reason having the ports on each CM connected to both switches will keep the SAN running in the event of a switch or port failure.  Regards, 
Hi, I would like to know what would cause the active controller to fail over to the passive controller. Here is a scenario:  Controller A eth0 is connected to switch A Controller A eth1 is connected to switch B Controller B eth0 is connected to switch A Controller B eth1 is connected to switch B  network switch A goes off line, would the controller A failover to controller B? network switch B goes off line, would the controller A failover to controller B? the port eth0 in switch A and the port eth1 in switch B goes offline. All other ports on the network switches A and B are up. Would the controller A fail over to controller B?  Many thanks, Oliver Leach
When will a controller fail over to the other controller?