A two-switch fabric is just that. The SAN consists of two switches implemented in a way that there is no single point of failure. Brocade, for example, offers a two-switch license for their eight- and 16-port switches. It is targeted to the SMB market as a low cost solution for organizations that may not need anything more than this type of configuration.
A full fabric consists of many switches can be interconnected in a mesh. Generally, this is also done to avoid the SAN going down due to a failure of an HBA, storage port, transceiver, cable, switch or a switch port.
Keep in mind that all directors allow you to create the logical equivalent of a two-switch configuration, but the cost would be much higher.
This was first published in May 2005