Each component of your disk assembly (the adapter bus, the device bus and cable, the disk controller, and the disk or disk cabinet) has a rate of maximum and expected throughput. The total configuration is limited to the maximum throughput of the slowest component, so it's important to find that value for your system. The booklets provided by the component manufacturer usually list maximum and expected transfer rates and throughput for each component.
The final components in your disk configuration are the applications that issue the I/O requests. They determine how the physical disks are used. In general, reading or writing a few large records is more efficient than reading or writing many small ones. This curve levels off when the disk is moving such large blocks of data that each transfer is slower, though its total throughput is quite high. Unfortunately, it is not always easy to control this factor. However, if your system is being used to transfer many small units of data, this inefficiency may help to explain, though not resolve, high disk use.
In this section, we'll show you how to test the efficiency of your disk configuration at reading and writing and at sequential versus random transfers. We'll also share some strategies for testing the maximum throughput of your disk, and point you to some files on the Windows NT Resource Kit 4.0 CD for testing disk throughput.