Managing Thermal Emergencies in Disk-Based Storage Systems

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 worst case by modulating the activities to avoid thermal emergencies caused by unexpected events, such as fan-breaks, increased inlet air temperature, etc. A delay-based approach to adjust the disk seek activities is one such DTM solution for 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. In this paper, we investigate the possibility of using a multispeed disk-drive (called dynamic rotations per minute (DRPM)), which 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 this DTM technique.