Adaptive Disk Spin-down Policies for Mobile Computers

Mobile computers typically spin down their hard disk after a fixed period of inactivity. If this threshold is too long, the disk wastes energy; if it is too short, the delay due to spinning the disk up again frustrates the user. Usage patterns change over time, so a single fixed threshold may not be appropriate at all times. Also, different users may have varying priorities with respect to trading off energy conservation against performance. We describe a method for varying the spin-down threshold dynamically by adapting to the user's access patterns and priorities. Adaptive spin-down can in some circumstances reduce by up to 50 the number of disk spin-ups that are deemed by the user to be inconvenient, while only moderately increasing energy consumption.