Storage Interfaces

Fibre Channel Topologies

There are three principal topologies supported by the Fibre Channel standard: point-to-point, arbitrated loop, and switched fabric. These topologies are analogous to the bus, ring, and star topologies encountered in traditional data networks. Each topology has unique features, advantages, and disadvantages.

Point-to-Point

Image: Point to Point topology Point-to-point is the simplest of the three topologies. It consists of only two Fibre Channel devices directly connected to each other. There is no sharing of the media, which allows the devices to enjoy the total bandwidth of the link.

Arbitrated Loop

Image: Aribitrated Loop topology Although similar to the ring network topology often associated with Token Ring networks, arbitrated loop should not be confused with a token-passing scheme. Unlike the token-passing method, which allows a device to communicate only when it has access to a token traveling around the ring, the arbitrated loop requires devices to arbitrate for access to the loop. Once control of the loop is granted, there is no limit on the amount of time that a device controls it. Devices on the loop share bandwidth. The arbitrated loop topology is often used inside Fibre Channel disk enclosures

Switched Fabric

Image: Switched Fabric topology The switched fabric topology employs Fibre Channel switches and provides the highest level of performance and connectivity in high end applications. Switched fabric can accommodate over 16 million devices, and Fibre Channel devices do not share bandwidth in this type of environment. Large SANs often use this topology.