Reducing disk I/O times using anticipatory movements of the disk head

Finding a good rest position for the disk head is very important for the performance of a hard disk. It has been shown in the past that rest positions obtained through anticipatory movements of the disk head can indeed improve response time, but practical algorithms have not been described yet. In this paper we describe a software technique for perfoming anticipatory movements of the disk head. In particular, we show that by partitioning the disk controller memory into a part used for caching and a part used for predictive movements, lower I/O times as compared with the usual read-ahead cache configurations are obtained. Through trace-driven simulations we show in fact that significant improvements in the disk I/O times can be obtained as compared to standard disk caching. Since the technique should be realized at the firmware level in the disk controller and no hardware modifications are needed, the implementation cost is low.