全程优化的固态硬盘垃圾回收方法

由于NAND闪存的固有限制，写前擦除和擦除粒度较大，基于NAND Flash的固态硬盘（SSD）需要执行垃圾回收以重用失效页。然而垃圾回收带来的高开销会显著降低SSD的性能，也会直接影响SSD的寿命。特别是对于频繁使用的有数据碎片的SSD，垃圾回收带来的性能下降问题将更为严重，现有的垃圾回收（GC）算法各自侧重垃圾回收操作的某个步骤，并没有给出全面考虑各步骤对整体影响的综合方案。针对该问题，在详细剖析垃圾回收过程的基础上，提出了一种全程优化的垃圾回收方法WPO-GC，在数据初始放置、垃圾回收目标块的选择、有效数据的迁移、触发回收的时间点以及中断处理方式上，尽可能全面地考虑各步骤对SSD正常读写请求和寿命的影响。通过开源模拟器SSDsim上的WPO-GC的有效性验证表明，同典型GC算法相比，WPO-GC可以减少SSD读请求延迟20%~40%和写请求延迟17%~40%，均衡磨损近30%。

Whole process optimized garbage collection for solid-state drives

Due to NAND flash' inherent restrictions like erase-before-write and a large erase unit, flash-based Solid-State Drives (SSD) demand garbage collection operations to reclaim invalid physical pages. However, the high overhead caused by garbage collection significantly decrease the performance and lifetime of SSD. Garbage collection performance will be more serious, especially when the data fragments of SSD are frequently used. Existing Garbage Collection (GC) algorithms only focus on some steps of the garbage collection operation, and none of them provids a comprehensive solution that takes into consideration all the steps of the GC process. On the basis of detailed analysis of the GC process, a whole process optimized garbage collection algorithm named WPO-GC (Whole Process Optimized Garbage Collection) was proposed, which integrated optimizations on each step of the GC in order to reduce the negative impact on normal read/write requests and SSD' lifetime at the greatest extent. Moreover, the WPO-GC was implemented on SSDsim which is an open source SSD simulator to evaluate its efficiency. The experimental results show that the proposed algorithm can decreases read I/O response time by 20%-40% and write I/O response time by 17%-40% respectively, and balance wear nearly 30% to extend the lifetime, compared with typical GC algorithm.