Chapter 3
Connecting Hosts
45
Using Host Port Interconnects
When the internal connections between host ports are enabled through RAIDar, host
port 0 on each controller is internally connected to host port 1 on the other
controller. This provides redundancy in the event one controller fails (failover) by
making volumes owned by the failed controller accessible on the surviving
controller.
Enable port interconnects when controller enclosures are attached directly to hosts
and high availability is required, or when switch ports are at a premium and fault
tolerance is required but highest performance is not.
When ports are not interconnected, volumes owned by a controller are accessible
from two of its host ports only. Use this default setting when controller enclosures
are attached through one or more switches, or when they are attached directly but
performance is more important than availability.
Using Loop or Point-to-Point Topology
R/Evolution 2730 FC Controller Enclosures use Fibre Channel Arbitrated Loop
(loop) topology by default.
Using loop topology enables hosts to see all volumes on all ports after failover. Use
loop topology, where possible, as it provides the most flexible and host-
independent, fault-tolerant configuration. Point-to-point topology restricts the ability
for the system to present volumes from both controllers after a failover, limiting the
overall configuration choices.
When ports are interconnected, you can use loop topology only. When ports are not
interconnected, you can use either loop or point-to-point topology.
Note –
Point-to-point topology is supported for switch attach configurations only.
For additional guidelines on connecting controller enclosures to hosts, refer to the
Best Practices Guide
. For information on placing and connecting enclosures safely,
refer to the
Site Planning Guide
. For information on how controllers present
volumes to data hosts, see the
Administrator's Guide
.
