22% Higher performance, 2x SCM write endurance heterogeneous storage with dual storage class memory and NAND flash

Storage class memories (SCMs); for instance, (STT-)MRAM, ReRAM, PRAM, and 3D XPoint, have much attention from storage systems. Each SCM has different characteristics, such as read/write latency, endurance, and bit cost. For example, MRAM has short latency and high endurance, but its cost is high. In contrast, ReRAM, PRAM, and 3D XPoint have lower endurance, but their cost is lower than MRAM. From these SCM characteristics, MRAM is classified into memory-type SCM (M-SCM), and ReRAM, PRAM, and 3D XPoint are called storage-type SCM (S-SCM). Previous studies show that SCM improves NAND flash based storage performance. However, cost of M-SCM is too high for storage usage. To bring out the best of M-SCM and S-SCM characteristics, this paper proposes a heterogeneous storage with two types of SCM, called dual SCM, and NAND flash memory. In the proposed storage, M-SCM stores very frequently accessed super-hot data and S-SCM stores hot data. By considering the storage performance and total storage cost, only 1% of M-SCM improves the storage performance by 22% and write endurance of S-SCM by 2 times compared with conventional S-SCM and NAND flash hybrid storage. With this storage configuration, M-SCM and S-SCM should have write cycles 3.2×102 and 4.5×101 times higher than MLC NAND flash.