Reorder Write Sequence by Hetero-Buffer to Extend SSD’s Lifespan
Reorder Write Sequence by Hetero-Buffer to Extend SSD’s Lifespan
复制标题
DOI：
10.1007/s11390-013-1309-5
复制
发表时间：
2013-02
影响因子：
0.7
通讯作者：
Zhiguang Chen;Nong Xiao;Fang Liu;Yimo Du
中科院分区：
文献类型：
--
作者：
Zhiguang Chen;Nong Xiao;Fang Liu;Yimo Du
寿命有限是基于 NAND 闪存的 SSD 的一大缺陷. NAND 闪存的两个特性降低了 SSD 的寿命, 一个是非定点更新, 另一个是同一物理块内的顺序写约束. SSD 通常采用写缓冲延长寿命. 但是, 现有的写缓冲策略一般只关注以上提到的第一个特性, 第二个特性被忽略. 本文提出一种异构的写缓冲, 同时兼顾以上两点. 该异构写缓冲由两部分组成, DRAM 和重排序区域. 其中, DRAM 主要用来取得较高的命中率, 以克服第一个缺陷; 冲排序区域主要用来对写请求冲排序, 以克服第二个缺陷. 该异构缓冲从两方面优于传统的写缓冲. 首先, DRAM 可以采用现有的任何好性能缓存替换策略, 可以取得较高的命中率; 其次, 该缓冲对写请求冲排序, 这是传统的写缓冲没有涉及到的. 除了以上提到的优化, 我们还考虑了 SSD 写缓冲的工作环境. 使该异构写缓冲的性能得到进一步的提升. 模拟实验证明, 对于大多数工作负载, 本文提出的异构写缓冲显然优于传统的写缓冲.Abstract: The limited lifespan is the Achilles' heel of solid state drives (SSDs) based on NAND flash. NAND flash has two drawbacks that degrade SSDs' lifespan. One is the out-of-place update. Another is the sequential write constraint within a block. SSDs usually employ write buffer to extend their lifetime. However, existing write buffer schemes only pay attention to the first drawback, while neglect the second one. We propose a hetero-buffer architecture covering both aspects simultaneously. The hetero-buffer consists of two components, dynamic random access memory (DRAM) and the reorder area. DRAM endeavors to reduce write traffic as much as possible by pursuing a higher hit ratio (overcome the first drawback). The reorder area focuses on reordering write sequence (overcome the second drawback). Our hetero-buffer outperforms traditional write buffers because of two reasons. First, the DRAM can adopt existing superior cache replacement policy, thus achieves higher hit ratio. Second, the hetero-buffer reorders the write sequence, which has not been exploited by traditional write buffers. Besides the optimizations mentioned above, our hetero-buffer considers the work environment of write buffer, which is also neglected by traditional write buffers. By this way, the hetero-buffer is further improved. The performance is evaluated via trace-driven simulations. Experimental results show that, SSDs employing the hetero-buffer survive longer lifespan on most workloads.