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Abstract

A system and method that utilize a scheduling algorithm to reorder queued I/O commands in rotating disk drives. The reordering is implemented by selecting commands based on a probabilistic approach that minimizes the expected next command access time. Thus, the scheduling algorithm allows data to be accessed in the shortest possible expected time, and maximizes the throughput of the drive. The scheduling algorithm improves the I/O average access time by estimating the expected access time (EAT) for the queued commands, and by reordering these commands so that the command with the least expected access time (LEAT) is executed first. The scheduling algorithm weights the possible access times of commands stored in the scheduling queue, and accounts for the probability of executing a command during a first possible revolution or cycle, as well as the probability of executing the command in the second possible revolution. Both of these probabilities are taken into consideration in reaching a final determination as to the queue order of the commands. This allows for taking calculated risks in scheduling commands so as to minimize long-term average latency.

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