Chapter 4. Fibre Channel SAN Topologies

Fibre Channel architecture has evolved three distinct physical topologies to support connectivity between networked devices: point-to-point, arbitrated loop, and fabric. The first Fibre Channel configurations were built on a dedicated, point-to-point connection between two nodes. Participants in a point-to-point topology establish an initial connection via login and then assume full bandwidth availability. Arbitrated loop allows more than two devices to communicate over a shared media. An initiator in a loop environment must negotiate for access to the media before launching a transaction. A Fibre Channel fabric topology provides multiple, concurrent, point-to-point connections via link-level switching, and so it entails a much higher level of complexity.

The vast majority of Fibre Channel SAN configurations being shipped today by major storage solutions providers are based on fabric switches. This chapter reviews the internal operations of point-to-point, loop, and fabrics, focusing on the requirements of the more commonly deployed switched fabrics.