Thermal-aware design of disk-drives is an important concern because high temperatures can cause reliability problems. Hence, Dynamic Thermal Management (DTM) has been proposed to operate the disk at the average case, rather than the worst case by modulating the activities to avoid thermal emergencies at run time while pushing the performance. A delay-based approach to adjust the disk seek activities is one DTM solution for normal disk-drives. Even if it 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 multi-speed disk-drive which dynamically modulates the rotational speed of the platter (called DRPM) for implementing DTM. Using a detailed performance and thermal simulator of storage system, we evaluate DTM policies and observe that the DRPM technique is the best to avoid thermal emergencies. However, we find that the time taken to transition between different rotational speeds of the disk is critical to the effectiveness of this DTM technique.