AN INVESTIGATION OF THE IMPACT OF DISK ACCESS TIME ON THE PERFORMANCE OF AN INTERACTIVE BUSINESS APPLICATION

In the complex situation of multiuser, interactive systems executing realistic (not completely disk intensive) tasks, the impact on system performance of small decreases in disk access speed is not readily apparent. This situation is common among systems using today's competitive hard disk drives. As a result of the absence of any published research to the contrary, many system integrators "play it safe" and purchase more expensive, higher speed drives. This results in higher system prices with no proven reward in terms of better "real world" application performance. The focus of this thesis is to provide empirical research to investigate this matter, with special emphasis on performance measurements that reflect the end-user perspective.; The experimental technique chosen consisted of constructing a workload model (the application, the users, and their demands on the system) and observing the test system as it processed the workload. A Remote Terminal Emulator was used to emulate users and measure the system's response as they interacted with it in the manner described by the test workload scripts. Response time and throughput were selected as the performance measures since they closely parallel end-user's perceptions of system performance.; Eight different tests were devised by varying the three main parameters of interest: file size, job mix, and number of users. The eight tests were run for each of two average disk access speeds, 33 and 45 milliseconds. The results showed that in this case, the impact of the disk speed change was overwhelmed by the other factors. Though the performance difference was measurable, it was of such a small magnitude as to be unnoticeable by system users.; These results have implications for both system integrators and disk drive manufacturers, who would now factor in smaller system performance gains for the higher cost, higher performance disk drives. Further work is needed in this area of Computer Performance Analysis to more clearly understand the impact of disk speed on complex systems, and to define those system environments and architectures that are most sensitive to disk access speed.