Compaq ProLiant 6500 Compaq Parallel Database Cluster Model PDC/O2000 for Orac - Page 63

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.