Storage Interfaces

Fibre Channel Operation

Data communication generally takes place on channels or networks. A channel provides either a direct or switched point-to-point connection between the communicating devices. A channel is typically hardware intensive and transports data at a high speed with low overhead. SCSI is an example of a channel.

In contrast, a network is an aggregation of distributed nodes (workstations, servers, or peripherals) with its own protocol, supporting interaction among these nodes. A network has a relatively high overhead since it is software intensive and, consequently, is slower than a channel. Networks can handle a more extensive range of tasks than channels as they operate in an environment of unanticipated connections, while channels operate among only a few devices with predefined addresses.

Fibre Channel attempts to combine the best attributes of these two methods of communication into a new I/O interface that meets the needs of both channel and network users. Fibre Channel is the general name of an integrated set of standards developed by the American National Standards Institute (ANSI).

NOTE Note: "Fibre" is the international spelling used for the Fibre Channel standard.

Fibre Channel is simply the transport vehicle for the supported command set, such as SCSI. It is unaware of the content of the information being transported. Fibre Channel simply packs the data into frames and transports them to the appropriate device. The encapsulated command set, SCSI commands in this case, is responsible for the accessing of data.

Fibre Channel vs. SCSI

Even though the SCSI command set can be encased in Fiber Channel, it should not be confused with the traditional parallel SCSI interface. Fibre Channel by and large overcomes SCSI's limitations.

Fibre Channel

SCSI


Performance	A serial interface that operates at 2 Gigabits per second.	A parallel interface that operates up to 160MB a second.

Devices	126 devices using loops or up to 16 million with a switched fabric.	16 devices per SCSI channel.

Availability	Allows addition or removal of devices without rebooting.	Generally the host server must be rebooted to recognize new devices.

Cabling	Can be either copper or fiber optic or a combination of both with lengths of 30m for copper and up to 10km for fiber optic.	Only copper cable is supported, with lengths of up to 25m.

Termination	No termination is required.	Termination is required.