SCM capacity and NAND over-provisioning requirements for SCM/NAND flash hybrid enterprise SSD

The required storage class memory (SCM) capacity and NAND over-provisioning (OP) for SCM/NAND hybrid enterprise solid state drive (SSD) are evaluated for various storage workloads. From the worst case simulations (hot and random data intensive workloads), it is found that less than 8% SCM/NAND capacity ratio with below 25% NAND OP is sufficient assuming SCM bit cost is 10-times as high as that of NAND. Other workloads with the exception of all-cold-data case can use less than 4% SCM/NAND capacity ratio with 100% NAND OP. According to the analyses, SCM tends to be cost-effective for the hot workload rather than the random one. Furthermore, the effect of NAND organization on the hybrid SSD write performance is considered. NAND organization with an 8-128KB page size and 1-8MB block size provides the best performance for the hot and random data intensive workloads. From the energy point of view, SCM/NAND hybrid SSD allows larger NAND page sizes compared with NAND-only SSD.