Technical data

Although the fabric topology is more expensive, it provides both increased
connectivity and higher performance; switches provide a full-duplex 100
(200) MB/sec point-to-point connection to the fabric. Switches also provide
improved performance and scaling because nodes on the fabric see only
data destined for themselves, and individual nodes are isolated from
reconfiguration and error recovery of other nodes within the fabric. Switches
can provide management information about the overall structure of the
Fibre Channel fabric, which may not be the case for an arbitrated loop hub.
Table 6–1 compares the fabric and arbitrated loop topologies.
Table 6–1: Fibre Channel Fabric and Arbitrated Loop Comparison
When to use Arbitrated Loop When to use Fabric
In clusters of up to two members In clusters of more than two members
In applications where low total solution
cost and simplicity are key requirements
In multinode cluster configurations when
possible temporary traffic disruption due
to reconfiguration or repair is a concern
In applications where the shared
bandwidth of an arbitrated loop
configuration is not a limiting factor
In high bandwidth applications where
a shared arbitrated loop topology
is not adequate
In configurations where expansion and
scaling are not anticipated
In cluster configurations where
expansion is anticipated and requires
performance scaling
6.3 Example Fibre Channel Configurations Supported by
TruCluster Server
This section provides diagrams of some of the configurations supported by
TruCluster Server Version 5.1A. Diagrams are provided for both transparent
failover mode and multiple-bus failover mode.
6.3.1 Fibre Channel Cluster Configurations for Transparent Failover
Mode
With transparent failover mode:
• The hosts do not know a failover has taken place (failover is transparent
to the hosts).
• The units are divided between an HSG80 port 1 and port 2.
• If there are dual-redundant HSG80 controllers, controller A port 1 and
controller B port 2 are normally active; controller A port 2 and controller
B port 1 are normally passive.
• If one controller fails, the other controller takes control and both its
ports are active.
6–8 Using Fibre Channel Storage