Real-Time Systems

Abstract

Thermal-aware design of disk drives is important because high temperatures can cause reliability problems. Dynamic Thermal Management (DTM) techniques have been proposed to operate the disk at the average case temperature, rather than at the worse case by modulating the activities to avoid thermal emergencies. The thermal emergencies can be caused by unexpected events, such as fan-breaks, increased inlet air temperature, etc. One of the DTM techniques is a delay-based approach that adjusts the disk seek activities, cooling down the disk drives. Even if such a DTM approach could overcome thermal emergencies without stopping disk activity, it suffers from long delays when servicing the requests. Thus, in this chapter, we investigate the possibility of using a multispeed disk-drive (called dynamic rotations per minute (DRPM)) that dynamically modulates the rotational speed of the platter for implementing the DTM technique. Using a detailed performance and thermal simulator of a storage system, we evaluate two possible DTM policies (- time-based and watermark-based) with a DRPM disk-drive and observe that dynamic RPM modulation is effective in avoiding thermal emergencies. However, we find that the time taken to transition between different rotational speeds of the disk is critical for the effectiveness of the DRPM basedmore » DTM techniques.« less