Fibre Channel Technology SCSI technology as a successor, with the former compared with the three main advantages: link distance, scalability and performance.
1. Connect the advantages of distance
We know, SCSI cable a maximum of 25m, which is still only a theoretical value. In practice, when the number of SCSI devices on the channel more than 8 hours, the connection distance is only limited to 1.5 ~ 3m. The distance of the connected Host Internal devices, have been enough. But now, more and more devices need to host an external connection. Used data backup tape library, two-machine cluster system Disk array These devices must be connected to an external host. When the host and the external storage device when the distance a little bit far, SCSI can not do anything.
I had a small Enterprise Ran into trouble this way, this company's offices and production centers have a certain distance, about 100m or so. Produce Environment And office environments have a server, through a system fault, the company recognized the importance of stability of the system, decided to adopt a two-machine cluster approach to protection of their IT System. Program quickly created - the use of existing two mutually redundant servers. But the problem came, 100m distance to the SCSI is too long. No matter which side of the shared disk array on the other side of the server can not connect to it.
In my recommendation, this enterprise was last used Fibre Channel disk array. On Fibre Channel technology, this problem can not be overemphasized, multi-mode fiber can reach 300 ~ 500m link distance, single-mode fiber can reach 10km.
2. Scalability advantages of fiber optic technology Another advantage is its strong scalability.
Arbitration in a fiber loop, you can connect 126 devices, and in an exchange-type structure, can accommodate more than 60,000 devices. In contrast, SCSI channel can only accommodate a maximum limit of 15 devices, has seriously affected the system upgrade scalability. Especially in the case of a large amount of data, Fibre Channel can be used as a relatively small access control chip, so that management is simple, fault point reduction, thus increasing system stability and reliability. In addition, the Fibre Channel devices can be switched through arbitration or loop structure, connected into a network, the so-called SAN. The SCSI technology can achieve point to point connections, making it impossible in some circumstances to meet the demand.
Example, in multi-machine cluster, in general, need to participate in all the host server cluster share the same disk array. At present, many clustering software can support as many as 32 or 64 hosts, through "a more prepared" or "multi-multi-prepared" approach to achieve high availability cluster. However, the mechanisms behind the connection, more than 2 hosts in the cluster environment, SCSI technologies simply can not achieve more than the host on the shared disk arrays connected.
3. Performance advantages
Finally, and most obvious point is that the high-performance fiber-optic technology. The current optical fiber technology Standard Has been developed to a single 200MB / s bandwidth, while the bandwidth of SCSI technology is usually 160MB / s, the latest SCSI standard provides 320MB / s bandwidth, the array controller based on this standard is not available yet. Comparing this value from the point of view though, 200MB / s and 160MB / s not much difference, and the new 320MB / s bandwidth SCSI technology looks even superior, but in actual use, the user will find fiber SCSI channel bandwidth than the bandwidth to be much higher, even several times in SCSI technology. Why? Is very simple, SCSI claims of 160MB / s Ye Hao, 320MB / s worth mentioning, are absolutely ideal conditions, a theoretical value, in the actual environment simply can not get this performance. Indeed 320MB / s of SCSI technology in a real environment can generally be 60 ~ 70MB / s performance, 160MB / s perf ormance of SCSI technology is slightly lower, probably in the 50MB / s or so. The Fibre Channel technology is different, in the optimized environment can be achieved nominal performance, even in ordinary circumstances, 200MB / s fiber-optic technology can be 150 ~ 190MB / s of the measured performance.
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