Reducing Disk Power Consumption in Servers with DRPM

T he growth of business enterprises and the Internet's emergence as a data processing medium have caused server-centric applications to proliferate. Data-centric services , such as file servers, Web portals, and transaction-processing systems have become commonplace in large corporations, smaller businesses, and academic institutions. Further, search engines such as Google and e-mail services like Hotmail sustain the Internet needs of millions each day. Until now, performance has been the primary objective when designing hardware and software for these servers. Processor and memory designers constantly aim for higher clock frequencies and try to pack as many transistors as possible onto a chip. Disk drive designers attempt to manufacture faster hard disks with denser storage capacity, while software architects tune their applications for peak performance on a given hardware platform. Recently, however, power dissipation has become a growing concern. Although traditionally considered a problem for mobile, battery-operated systems , power also poses challenges in terms of electricity costs and overall system design and reliability. Power can put a limit on how much designers can push performance, as power dissipation generates heat that affects component stability and reliability, especially for large server systems. The input/output subsystem expends a significant percentage of this power. Servers use disk arrays, a large collection of disks that sustain the data requirements of these systems and, in many cases, exert a significant impact on overall server performance. Therefore, developers configure disk arrays to deliver extremely high performance. Although effective techniques exist for tackling disk power for laptops and workstations, applying them in a server environment presents a considerable challenge , especially under stringent performance requirements. Using dynamic rotations per minute (DRPM) speed control for power management in server disk arrays can provide large savings in power consumption with very little perturbation in delivered performance. The DRPM technique dynamically modulates the hard-disk rotation speed so that the disk can service requests at different RPMs. Better still, existing technology can overcome the fundamental engineering challenges that fabricating such a device presents. Typically, organizations house server machines in data centers, which are designed to supply high-quality electric power to those servers via multiple feed lines and extensive backup power supplies. 1 Further, to ensure the thermal stability of the servers, data centers employ powerful heating, ventilation, and airconditioning systems. The power distribution in a typical server system allocates fully 40 percent of the overall power to the cooling system. Nevertheless, among …