Fiber channel technology as a successor of SCSI technology, compared with the former, mainly has three advantages: connection distance, scalability and performance.
We all known that the SCSI fiber optic patch cable do not exceed 25 m, which is just a theoretical value. In practice, when the SCSI channels more than eight, the connected normally only limit the distance in 1.5 ~ 3 m. The distance for equipment connection within the host, is enough. But now, more and more equipment need to host external connections. Data backup tape libraries, used by fleet set the disk array system, these devices must be connected to the outside of the host. When the host and external storage devices is slightly far, SCSI is powerless.
Extension ability is another advantage of Fiber Channel Technology. On a fiber loopback , 126 devices can be connected in a switching structure, can accommodate more than 60000 devices. SCSI channel, by contrast, most can only accommodate 15 equipment limited, seriously affected the system upgrade expansion ability. Especially in the case of a large amount of data, as a result of fiber channel can be used in a relatively small number of channel control chip, make its management mode is simple, the point of failure is reduced, thereby increasing the stability and reliability of the system.
In addition, the structure of fiber channel devices can loopback by arbitration or switched, connected into a network, known as the SAN. And SCSI technology can realize the point-to-point connection, making it in some circumstances cannot meet the demand.
Last but not the least, that is the high performance of optical fiber technology. The fiber optic network technology standards have been developed by the bandwidth of the single channel 200 MB/s, and the bandwidth of the SCSI technology usually is 160 MB/s, the latest SCSI standard provides the bandwidth of the 320 MB/s, based on the standard array controller hasn’t listed. Although numerical comparison from this point of view, 200 MB/s and the 160 MB/s is not too big difference, and the new 320 MB/s bandwidth SCSI technology look even better, but in actual use, a user will find that the bandwidth of the fiber channel is much higher than the bandwidth of the SCSI, or even several times the SCSI technology.
Actually 320 MB/s SCSI technology in a real environment can generally get 60 ~ 70 MB/s performance, 160 MB/s SCSI technology performance is slightly lower, will be about 50 MB/s. The fiber channel technology is different, in the environment of the optimized can completely achieve the nominal performance index, even in the ordinary environment, 200 MB/s optical fiber technology is also can be the measured performance of 150 ~ 190 MB/s.