Disk drive roadmap from the thermal perspective: a case for dynamic thermal management

The importance of pushing the performance envelope of disk drives continues to grow, not just in the server market but also in numerous consumer electronics products. One of the most fundamental factors impacting disk drive design is the heat dissipation and its effect on drive reliability, since high temperatures can cause off-track errors, or even head crashes. Until now, drive manufacturers have continued to meet the 40% annual growth target of the internal data rates (IDR) by increasing RPMs, and shrinking platter sizes, both of which have counter-acting effects on the heat dissipation within a drive. As this paper shows, we are getting to a point where it is becoming very difficult to stay on this roadmap. This paper presents an integrated disk drive model that captures the close relationships between capacity, performance and thermal characteristics over time. Using this model, we quantify the drop off in IDR growth rates over the next decade if we are to adhere to the thermal envelope of drive design. We present two mechanisms for buying back some of this IDR loss with dynamic thermal management (DTM). The first DTM technique exploits any available thermal slack, between what the drive was intended to support and the currently lower operating temperature, to ramp up the RPM. The second DTM technique assumes that the drive is only designed for average case behavior, thus allowing higher RPMs than the thermal envelope, and employs dynamic throttling of disk drive activities to remain within this envelope.