Compaq Parallel Database Cluster Model PDC/O2000 for Oracle8i and Windows 2000 Administrator Guide

Cluster Architecture 2-39
I/O Path Configurations for Redundant
Fibre Channel Arbitrated Loops
Overview of FC-AL SAN Topology
Fibre Channel standards define a multi-layered architecture for moving data
across the storage area network (SAN). This layered architecture can be
implemented using the Fibre Channel Fabric or the Fibre Channel Arbitrated
Loop (FC-AL) topology. The PDC/O2000 supports both topologies.
A redundant FC-AL is two to four FC-AL Switches or Storage Hubs installed
between Fibre Host Adapters in a PDC/O2000’s cluster nodes and the array
controllers in the shared storage subsystems. These hardware components
cannot be shared by other redundant FC-ALs or redundant Fibre Channel
Fabrics in the same cluster.
When Storage Hubs are used, the FC-AL SAN is a shared gigabit transport
with a total 100 MBps bandwidth divided among all Storage Hub ports. The
functional bandwidth available to any one device on a Storage Hub port is
determined by the total population on the segment and the level of activity of
devices on other ports. The more devices used, the less bandwidth that is
available for each port.
When FC-AL Switches are used, the FC-AL SAN supports multiple
100 MB/sec point-to-point connections in parallel. Each FC-AL Switch
provides multiple dedicated, non-blocking connections between Fibre Host
Adapters and array controllers (as contrasted with the shared connections on a
Storage Hub). The FC-AL Switch also eliminates the shared bandwidth speed
limitations of the Storage Hub.