Migration-Resistant Policies for Probe-Wear Leveling in MEMS Storage Devices

Abstract

Probes (read/write heads) in a MEMS storage device are susceptible to wear. We study probe wear, and analyze the causes of uneven wear. We show that under real-world workloads some probes can wear one order of magnitude faster than others. This premature expiry has severe consequences for reliability, timing performance, energy efficiency, and lifetime. Wear leveling precludes premature expiry and is thus necessary. We discuss the fundamental differences between probe wear in MEMS storage and medium wear in Flash, calling for a different treatment. We devise three policies to level probe wear. The policies provide a spectrum between best lifetime and least influence on the response time and energy efficiency of a MEMS storage device. We make the case that data migration can be prevented by augmenting the policies with a simple rule. We study the influence of the data layout configuration on the leveling performance of the policies.