Hybrid nonvolatile disk cache for energy-efficient and high-performance systems

NAND flash memory has been employed as disk cache in recent years. It has the advantages of high performance, low leakage power, and cost efficiency. However, flash memory's performance is limited by the inability of in-place updates, coarse access granularity, and a limited number of write/erase times. In this article, we propose a hybrid nonvolatile disk cache architecture for high-performance and energy-efficient systems, where the disk cache is implemented with a small-size phase change memory (PCM) and a largesize NAND flash memory. Compared with current flash memory-based disk cache, it has the following advantages. (1) System performance is improved as requests are carefully directed between PCM and flash memory; (2) the energy consumption of disk cache is substantially reduced with significant reduction of additional operations, such as garbage collections; (3) the efficiency of flash memory is improved with the reduction of write activities on flash memory; and (4) lifetime of NAND flash memory is increased with most of the write operations assigned to PCM, where PCM's lifetime is guaranteed to be longer than the lifetime of flash memory. Simulation results show that the proposed methods can substantially improve the system performance, energy consumption, and lifetime of the hybrid disk cache.