Quantitative Analysis of Disk Drive Power Management
in Portable Computers
Kester Li, Roger Kumpf, Paul Horton, and Thomas Anderson
Computer Science Division
University of California
Berkeley, CA 94720
With the advent and subsequent popularity of portable computers, power
management of system components has become an important issue.
Current portable computers implement a number of power reduction
techniques to achieve a longer battery life. Included among these is
spinning down a disk during long periods of inactivity. In this
paper, we perform a quantitative analysis of the potential costs and
benefits of spinning down the disk drive as a power reduction
technique. Our conclusion is that almost all the energy consumed by a
disk drive can be eliminated with little loss in performance.
Although on current hardware, reliability can be impacted by our
policies, the next generation of disk drives will use technology (such
as dynamic head loading) which is virtually unaffected by repeated
spinups. We found that the optimal spindown delay time, the amount of
time the disk idles before it is spun down, is 2 seconds. This
differs significantly from the 3-5 minutes in current practice by
industry. We will show in this paper the effect of varying the
spindown delay on power consumption; one conclusion is that a 3-5
minute delay results in only half of the potential benefit of spinning
down a disk.
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