Communicator e3000 MPE/iX Release 7.5 (Software Release C.75.00) (30216-90336)

Chapter 4

Fibre Channel Device and Adapter Support on HP e 3000 Systems

Fibre Channel Device Adapter Support

Since a fabric topology is complex and costlier, fibre channel technology allows FC devices to be connected in a

rather simpler topology called the Arbitrated Loop or Private Loop topology. A private loop is just a ring-like

connection of FC devices and host systems, with each entity physically connected only to its adjacent one on

either side. It forms a loop because communication between any two entities will have to pass through all

intermediate ones. In such a simpler topology, each host or device is identified simply by a Loop ID.

Figure 4-4 Fibre Channel Private Loop

A private loop topology allows up to 126 nodes to be connected. The Loop ID of FC devices can be set through

dial settings on the device itself. The Loop ID for host adapters is attained automatically through the fibre

channel initialization process. A private loop topology can be formed by connecting adjacent nodes to each

other directly or by interconnecting them through an FC Hub. The hub internally connects the receive and

transmit wires of adjacent nodes to form the loop. The main advantage of using hub is that it electrically

bypasses inactive ports, thus allowing loop communication to happen even if any of the nodes goes faulty.

There is also another variant of the arbitrated loop topology called Public Loop which results when an FC

switch is introduced as part of an arbitrated loop. But as far as fibre channel protocol is concerned, this is

considered to be covered under the fabric topology itself.

Another simpler topology is the Point-to-Point topology where a single device is connected to a single host by

means of a direct connection. Some fibre channel protocol operations followed in a “point-to-point” topology is

different from the private loop and fabric topologies.

Figure 4-5 Fibre Channel Point-to-Point

Fibre Channel Private Loop (without Hub) Fibre Channel Private Loop (with Hub)

Host

Device

Host Device

Host

FC Hub

Host

Device Device

Device

Fibre Channel Point-to-Point

Host Device