Fibre Channel, SCSI and You

For a more sophisticated test, we used BlueCurve's Dynameasure benchmarking tool to test the networks' performance. (For more information about this tool and the benchmarks we used, see Carlos Bernal, "Dynameasure Enterprise 1.5 by BlueCurve," page 81.) Because we were working with alpha and beta FC products, we kept our tests simple and used the SQL and File transfer benchmarks to look only at whether FC offers a performance advantage.

For the SQL benchmark, we used the Order Entry/Single Read/Write and Order Entry/Mixed Read/Write tests with a 96MB dataset. For the File benchmark, we used the Copy All Bi-directional benchmark, which copies a random mix of files; the file dataset size was 35.6MB. We used 20 client systems in a five-step test that simulated 20 to 100 users.

FC and SCSI-3 performed about the same in the SQL test, as you see in Table 1 . In the file transfer test, we found FC to be 10 percent to 20 percent faster than SCSI-3, as you see in Table 2. This result is much different from the 265 percent that you might expect. Of course, performance is subject to change with the final releases of the hardware components and software drivers.

So, why wasn't FC faster? Perhaps the hard drives couldn't spit out data fast enough, or the FC card in the server couldn't pump data into memory fast enough, or the CPUs couldn't take the data out of memory and dump it back to the FC card fast enough, or a combination of these factors. This situation is analogous to the difference between a 10Mbps and a 100Mbps Ethernet: The performance doesn't increase 10 times when you move from 10Mbps to a 100Mbps network, only about 2.5 times. The speed of the wire (the transfer rate) is only one of many factors that come into play when you interconnect equipment.

Today, FC can connect more devices and give you an extra bit of performance over SCSI-3, although you can approach FC's speed and connectivity by using multiple SCSI controllers. FC costs more now because it is new technology, but its costs are already coming down. If you need the fault tolerance of RAID, you can buy hardware-based SCSI RAID controllers, which are much faster than software-based RAID, thus making a multichannel SCSI solution a better solution than FC for many applications. But tomorrow will bring hardware-based FC RAID solutions and FC-to-SCSI converters. Then FC will be more attractive.