System and method for scheduling of random commands to minimize impact of locational uncertainty

摘要

A system and method are provided for hard disk drive command queue ordering with locational uncertainty of commands. For each command in the hard disk drive command queue, an expected access time is calculated utilizing a probability distribution for a currently executing command and a probability distribution for a candidate command. A command in the hard disk drive command queue having a minimum calculated expected access time is identified. Then the identified command having a minimum calculated expected access time is executed. The probability distribution for a currently executing command represents an ending location distribution for the currently executing command. The probability distribution for a candidate command represents a starting location distribution for the candidate command. For an estimated seek time of less than a time for one full revolution, a probability of a miss multiplied by a time of one extra revolution and multiplied by a candidate arrival probability is calculated and the result is added to an estimated seek time to provide the expected access time. For an estimated seek time of greater than a time for one full revolution, a probability of a make multiplied by a time of one extra revolution and multiplied by a candidate arrival probability is calculated and the result is subtracted from an estimated seek time to provide the expected access time.