Three Advantages of Fiber Channel Technology Access

Advantages of Optical Fiber

As the successor of SCSI technology, fiber channel technology has three main advantages compared with its predecessor: Connection distance, scalability and performance.

1. Advantages of connection distance

We all know that SCSI Cables cannot exceed 25 m at most, and this is only a theoretical value. In practice, when the number of devices on the SCSI channel exceeds 8, the connection distance is generally only limited to 1.5 ~ 3 m. This distance is sufficient for devices connected to the host. However, more and more devices need to be connected outside the host. The tape library used for data backup and the disk array of the dual-host cluster system must be connected outside the host. SCSI is powerless when the distance between the host and external storage devices is a little long.

I once encountered such a problem in a small enterprise. The office building of this enterprise is about m away from the production center. The production environment and office environment each have one server. After a system failure, the company realized the importance of system stability and decided to adopt a dual-host cluster to protect its IT systems. The solution soon came into being-two existing servers were used for mutual backup. But the problem is that the m distance is too long for SCSI. No matter which side the shared disk array is placed, the servers on the other side cannot connect to it.

In my recommendation, the company finally adopted a fiber channel disk array. For the fiber channel technology, the problem is naturally caused by the fact that multimode optical fiber cables can reach 300 ~ M connection distance, single-mode optical cable can reach 10 km.

2. Another advantage of optical fiber technology is its powerful scalability.

In an optical fiber arbitration loop, 126 devices can be connected, while in an exchange structure, more than 60 thousand devices can be connected. In contrast, the SCSI channel can accommodate a maximum of 15 devices, seriously affecting the system upgrade and expansion capabilities. Especially in the case of large data volumes, Because Fiber Channel can use a relatively small number of channel control chips, the management method is simple and fault points are reduced, thus increasing the system stability and reliability. In addition, Fiber Channel devices can connect to a network, called a SAN, through an arbitration loop or an exchange structure. The SCSI technology can only achieve point-to-point connections, which makes it unable to meet requirements in some environments.

For example, in a multi-host cluster environment, all the host servers involved in the cluster need to share the same disk array. Currently, many cluster software supports up to 32 or even 64 hosts, and supports high-availability clusters by means of "one-to-many" or "Multiple-to-many. However, due to the backward Connection Mechanism, in a cluster environment with more than two hosts, the SCSI technology cannot achieve multi-host shared connection to the disk array.

3. Performance advantages

Finally, the most prominent point is the high performance of the optical fiber technology. Currently, the optical fiber technology standard has been developed to a single channel bandwidth of 200 MB/s, while the SCSI technology bandwidth is usually 160 MB/s. The latest SCSI standard provides a bandwidth of 320 MB/s, this standard-based array controller is not available yet. Although there is no big difference between 200 Mbit/s and 160 Mbit/s, and the new 320 Mbit/s SCSI technology looks better, however, in actual use, users will find that the bandwidth of the fiber channel is much higher than that of the SCSI, or even several times higher than that of the SCSI technology. Why? In fact, it is very simple. The 160 Mbit/s or 320 Mbit/s declared by SCSI are all theoretical values under absolute ideal conditions, such performance cannot be achieved in the actual environment. In fact, the SCSI Technology of 320 Mbit/s can get 60 ~ 70 MB/S performance, 160 Mb/s SCSI technology performance is slightly lower, about 50 MB/S. However, the fiber channel technology is different. In an optimized environment, the performance indicators can be fully achieved. Even in a normal environment, the 200 Mbit/s fiber technology can be 150 ~ Measured performance of 190 Mb/s.

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