Maximizing Peformance/cost Figure of Merit of Storage-type SCM based SSD by Adding Small Capacity of Memory-type SCM

Non-volatile memories called “storage class memories (SCMs)” attract attentions to realize high-performance solidstate drive (SSD). Although storage-type SCM (S-SCM) based SSD has already appeared, memory-type (M-SCM) based SSD has not been realistic yet due to the high memory cost. This paper proposes multi-SCM SSD with M-SCM as non-volatile cache of S-SCM to improve the SSD performance. In addition, the best configuration of multi-SCM SSD is discussed to balance the cost and the performance. As a result, the optimal capacity of M-SCM improves the SSD performance by up to 134% with 12% cost increase. If either M-SCM or S-SCM reaches the endurance limit, multi-SCM SSD cannot be used any longer. The optimal utilization scenario is that write erase (W/E) cycles of both M-SCM and S-SCM become their limits at the same time. To boost the SSD performance, the impact of omitting wear-leveling from both SCMs are investigated. As a result, the performance enhances by up to 28.2%. Additionally, effective wear-leveling policy is considered to balance both SSD performance and its lifetime.