Integrated Write Buffer Management in Solid State Drives

Abstract

While NAND flash memory is used in a variety of end user devices, it has a few disadvantages, such as asymmetric speed of read and write operations, inability to in place updates, among others. Therefore random write within SSD is still far slower than sequential read/write and random read. To overcome these problems, various flash aware strategies have been suggested in terms of buffer cache, file system, FTL and others. Also, the recent development of next generation nonvolatile memory types such as MRAM, FeRAM and PRAM provide higher commercial value to Non-Volatile RAM (NVRAM). At today’s prices, however, they are not yet cost effective. Firstly, we suggest the utilization of small sized, next generation NVRAM as a write buffer to improve the overall performance of NAND flash memory based storage systems. We propose various block based NVRAM write buffer management policies and evaluate the performance improvement of NAND flash memory based storage systems under each policy. Also we propose a novel write buffer aware flash translation layer algorithm, optimistic FTL, which is designed to harmonize well with NVRAM write buffers. In this proposal, while log blocks are managed by the Flash Translation Layer (FTL), write buffer management has been treated separately from the FTL. Write buffer management schemes did not use the exact status of log blocks, and log block management schemes in FTL did not consider the behavior of the write buffer management scheme. So we demonstrates that log blocks and write buffers maintain a tight relationship, which necessitates integrated management to both of them. Since log blocks can also be viewed as another type of write buffer, we can manage both of them as an integrated write buffer. Then we propose an Integrated Write buffer Management scheme (IWM), which collectively manages both the write buffer and log blocks. We are then able to show, through extensive simulation, that the proposed scheme greatly outperforms previous schemes in terms of write amplification, block erase count, and execution time.