DISK DESIGN-SPACE EXPLORATION IN TERMS OF SYSTEM-LEVEL PERFORMANCE, POWER, AND ENERGY CONSUMPTION
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To make the common case fast, most studies focus on the computation phase of applications in which most instructions are executed. However, many programs spend significant time in the I/O intensive phase due to the I/O latency. To obtain a system with more balanced phases, we require greater insight into the effects of the I/O configurations to the entire system in both performance and power dissipation domains.
Due to lack of public tools with the complete picture of the entire memory hierarchy, we developed SYSim. SYSim is a complete-system simulator aiming at complete memory hierarchy studies in both performance and power consumption domains.
In this dissertation, we used SYSim to investigate the system-level impacts of several disk enhancements and technology improvements to the detailed interaction in memory hierarchy during the I/O-intensive phase. The experimental results are reported in terms of both total system performance and power/energy consumption. With SYSim, we conducted the complete-system experiments and revealed intriguing behaviors including, but not limited to, the following:
During the I/O intensive phase which consists of both disk reads and writes, the average system CPI tracks only average disk read response time, and not overall average disk response time, which is the widely-accepted metric in disk drive research.
In disk read-dominating applications, Disk Prefetching is more important than increasing the disk RPM. On the other hand, in applications with both disk reads and writes, the disk RPM matters.
The execution time can be improved to an order of magnitude by applying some disk enhancements. Using disk caching and prefetching can improve the performance by the factor of 2, and write-buffering can improve the performance by the factor of 10. Moreover, using disk caching/prefetching and the write-buffering techniques in conjunction can improve the total system performance by at least an order of magnitude.
Increasing the disk RPM and the number of disks in RAID disk system also have an impressive improvement over the total system performance. However, employing such techniques requires careful consideration for trade-offs in power/energy consumption.