NS-FTL: Alleviating the Uneven Bit-Level Wearing of NVRAM-based FTL via NAND-SPIN

Abstract

Non-Volatile random access memory (NVRAM) has been regarded as a promising DRAM alternative with its nonvolatility, near-zero idle power consumption, and byte addressability. In particular, some NVRAM devices, such as Spin Torque Transfer (STT) RAM, can provide the same or better access performance and lower power consumption when compared with dynamic random access memory (DRAM). These nice features make NVRAM become an attractive DRAM replacement on NAND flash storage for resolving the management overhead of the flash translation layer (FTL). For instance, when adopting NVRAM for storing the mapping entries of FTL, the overheads of loading and storing the mapping entries between the non-volatile NAND flash and the volatile DRAM can be eliminated. Nevertheless, due to the limited lifetime constraint of NVRAM, the bit-level update behavior of FTL may lead to the issue of uneven bit-level wearing and the lifetime capacity of those less-worn NVRAM cells could be underutilized. Such an observation motivates this study to utilize the emerging NAND-like Spin Torque Transfer memory (NAND-SPIN) for alleviating the uneven bit-level wearing of NVRAM-based FTL and making the best of the lifetime capacity of each NAND-SPIN cell. The experimental results show that the proposed design can effectively avoid the uneven bit-level wearing, when compared with page-based FTL on NAND-SPIN.