Characterizing the impact of process variation on write endurance enhancing techniques for non-volatile memory systems

Much attention has been given recently to a set of promising non-volatile memory technologies, such as PCM, STT-MRAM, and ReRAM. These, however, have limited endurance relative to DRAM. Potential solutions to this endurance challenge exist in the form of fine-grain wear leveling techniques and aggressive error tolerance approaches. While the existing approaches to wear leveling and error tolerance are sound and demonstrate true potential, their studies have been limited in that i) they have not considered the interactions between wear leveling and error tolerance and ii) they have assumed a simple write endurance failure model where all cells fail uniformly. In this paper we perform a thorough study and characterize such interactions and the effects of more realistic non-uniform endurance models under various workloads, both synthetic and derived from benchmarks. This study shows that, for instance, variability in the endurance of cells significantly affects wear leveling and error tolerance mechanisms and the values of their tuning parameters. It also shows that these mechanisms interact in subtle ways, sometimes cancelling and sometimes boosting each other's impact on overall endurance of the device.