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12 EF2915 Series User Guide
Chapter 2: The EF2915 Series Storage System
Fibre Channel Overview
Fibre Channel Topologies
There are three Fibre Channel network topologies, the simplest and least expensive of
which is the point-to-point topology. The second topology is the arbitrated loop which is
more complex and expensive than point-to-point and offers much more functionality. The
third topology is the fabric which offers the most functionality and is the most complex
and expensive. These different Fibre Channel typologies are described below.
Point-to-Point
This topology involves only two devices which are usually a server and a storage device,
with no devices existing between them. This topology is found in first generation
implementations of Fibre Channel.
Arbitrated Loop
This topology involves multiple devices that share a common medium. Not only does this
topology involve many more devices than point-to-point, but each device must arbitrate
for access and use of the shared medium. Arbitration ensures that the devices gain access
to and use the shared medium in an orderly and controlled manner. This topology is
similar to Token Ring in networking.
Fabric
This topology involves numerous devices but is characterized by having one or more Fibre
Channel switches in the same network. The storage devices announce or register their
presence on the fabric to the switches using the SNS (simple name server) databases that
reside on the servers. The SNS database includes the device’s network address, WWN
(world wide name), and other information that helps identify the device.
In order for the servers to know the number and location of the storage devices on the
network, each server queries the SNS database to discover the storage devices (switches
exchange SNS data so that each server has the information to discover the storage devices
on the network).
Types of Fibre Channel Ports
There are three basic Fibre Channel port types: the N_Port, the F_Port, and the E_Port.
Once arbitrated loop capabilities are added, the port names change to reflect this. These
ports are described below.
•
N_Port : A node port, or a port on a Fibre Channel disk or computer. These types of
ports only communicate with another N_Port on a different node, or with a switch.
•
F_Port : A fabric port (these can only be switch ports). These types of ports can only
be connected to an N_Port in a point-to-point connection.