The topology only affects how mapped volumes and port WWNs are presented if
one controller fails. Whichever topology is used, each data host has dual-ported
access to volumes through both controllers.
Failover in a switch attach, loop configuration.
If one controller fails in a
switch attach configuration using loop topology, the host ports on the surviving
controller present the port WWNs for both controllers. Each controller’s mapped
volumes remain accessible.
Failover in a switch attach, point-to-point configuration.
If one controller fails
in a switch attach configuration using point-to-point topology, the surviving
controller presents its mapped volumes on its primary host port and the mapped
volumes owned by the failed controller on the secondary port.
In a high-availability configuration, two data hosts connect through two switches to
a dual-controller storage system and the host port interconnects are disabled.
The following figure shows how port WWNs and mapped volumes are presented
when both controllers are active.