Policies for probe-wear leveling in MEMS-based storage devices

Probes (or read/write heads) in MEMS-based storage devices are susceptible to wear. We study probe wear, and analyze the causes of probe uneven wear. We show that under real-world traces some probes can wear one order of magnitude faster than other probes leading to premature expiry of some probes. Premature expiry has severe consequences for the reliability, timing performance, energy-efficiency, and the lifetime of MEMS-based storage devices. Therefore, wear-leveling is a must to preclude premature expiry. We discuss how probe wear in MEMS-based storage is different from medium wear in Flash, calling for a different treatment. We present three policies to level probe wear. By simulation against three real-world traces, our work shows that an inevitable trade-off exists between lifetime, timing performance, and energy efficiency. The policies differ in the size of the trade-off. One of the policies maximizes the lifetime, so that it is optimal; and the other two are less optimal, and are used based on the configuration of the device.