Enabling Intra-Plane Parallel Block Erase in NAND Flash to Alleviate the Impact of Garbage Collection
Enabling Intra-Plane Parallel Block Erase in NAND Flash to Alleviate the Impact of Garbage Collection
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DOI：
10.1145/3218603.3218627
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发表时间：
2018-07
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通讯作者：
Tyler Garrett;Jun Yang;Youtao Zhang
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作者：
Tyler Garrett;Jun Yang;Youtao Zhang
NAND闪存中的垃圾收集（GC）会将有效数据复制到其他位置，从而阻止传入的I/O请求，从而显著降低SSD中的I/O性能。为了帮助提高性能，NAND闪存利用各种高级命令来增加内部并行性。目前，这些命令仅跨通道、芯片、管芯和平面并行化操作，由于可能通过引入错误而损害有效数据的干扰风险而忽略了块级。然而，由于NAND闪存平面架构的三阱结构，可以并行地擦除平面内的多个块，而不会降低有效数据的完整性。可以限制由于多次块擦除而导致的页面移动的数量，以便限制每个GC的开销。此外，每个GC可以回收更多的容量，这会延迟未来的GC并有效地降低其频率。这样的Intra-Plane Parallel Block Cache（IPPBE）反过来减少了GC对传入请求的影响，从而改善了响应时间。实验结果表明，IPPBE可以使GC执行时间平均减少50.7%和33.6%，读/写响应时间平均分别减少47.0%/45.4%和16.5%/14.8%，页面移动平均减少52.2%和26.6%，块擦除平均减少14.2%和3.6%。能量分析表明，通过减少页面复制次数和块擦除次数，垃圾收集的能量成本平均可降低44.1%和19.3%。
Garbage collection (GC) in NAND flash can significantly decrease I/O performance in SSDs by copying valid data to other locations, thus blocking incoming I/O requests. To help improve performance, NAND flash utilizes various advanced commands to increase internal parallelism. Currently, these commands only parallelize operations across channels, chips, dies, and planes, neglecting the block level due to risk of disturbances that can compromise valid data by inducing errors. However, due to the triple-well structure of the NAND flash plane architecture, it is possible to erase multiple blocks within a plane, in parallel, without diminishing the integrity of the valid data. The number of page movements due to multiple block erases can be restrained so as to bound the overhead per GC. Moreover, more capacity can be reclaimed per GC which delays future GCs and effectively reduces their frequency. Such an Intra-Plane Parallel Block Erase (IPPBE) in turn diminishes the impact of GC on incoming requests, improving their response times. Experimental results show that IPPBE can reduce the time spent performing GC by up to 50.7% and 33.6% on average, read/write response time by up to 47.0%/45.4% and 16.5%/14.8% on average respectively, page movements by up to 52.2% and 26.6% on average, and blocks erased by up to 14.2% and 3.6% on average. An energy analysis conducted indicates that by reducing the number of page copies and the number of block erases, the energy cost of garbage collection can be reduced up to 44.1% and 19.3% on average.