GSSA: A Resource Allocation Scheme Customized for 3D NAND SSDs
GSSA: A Resource Allocation Scheme Customized for 3D NAND SSDs
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DOI：
10.1109/hpca51647.2021.00043
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发表时间：
2021-02
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通讯作者：
Chun-Yi Liu;Yunju Lee;Wonil Choi;Myoungsoo Jung;M. Kandemir;C. Das
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作者：
Chun-Yi Liu;Yunju Lee;Wonil Choi;Myoungsoo Jung;M. Kandemir;C. Das
由于程序复杂性的增加，基于3D NAND的SSD的高密度带来了更长的写入延迟。为了解决这种写入性能下降的问题，NAND闪存制造商实现了3D NAND特定的全序列编程（FSP）操作。FSP可以以与基线编程操作相同的延迟同时将多位信息编程到单元中，从而显著提高写入性能。然而，在SSD固件中直接采用（大粒度）FSP操作可能导致寿命退化问题，其中小写入被放大到大粒度，具有相当大比例的空数据。由于来自主机的“同步”命令阻止DRAM缓冲区积累足够的写入数据，因此SSD中的DRAM缓冲区无法完全缓解此问题。为了解决这个FSP引起的性能/寿命困境，在这项工作中，我们提出并评估GSSA（广义和专业扰码分配），一种新的写数据分配方案在SSD固件，它既考虑了各种3D NAND程序操作和内部3D NAND闪存架构。通过采用GSSA，SSD可以享受FSP带来的性能优势，而不会过度消耗寿命。我们的实验评估表明，GSSA可以实现的吞吐量和花费的生命周期的最佳性能和最佳的单粒度计划，分别。
The high density of 3D NAND-based SSDs comes with longer write latencies due to the increasing program complexity. To address this write performance degradation issue, NAND flash manufacturers implement a 3D NAND-specific full-sequence program (FSP) operation. The FSP can program multiple-bit information into a cell simultaneously with the same latency as the baseline program operation, thereby dramatically boosting the write performance. However, directly adopting the (large granularity) FSP operation in SSD firmware can result in a lifetime degradation problem, where small writes are amplified to large granularities with a significant fraction of empty data. This problem cannot completely be mitigated by the DRAM buffer in the SSDs since the “sync” commands from the host prevent the DRAM buffer from accumulating enough written data. To solve this FSP-induced performance/lifetime dilemma, in this work, we propose and evaluate GSSA (Generalized and Specialized Scramble Allocation), a novel written-data allocation scheme in SSD firmware, which considers both various 3D NAND program operations and the internal 3D NAND flash architecture. By adopting GSSA, SSDs can enjoy the performance benefits brought by the FSP without excessively consuming the lifetime. Our experimental evaluations reveal that GSSA can achieve the throughput and the spent-lifetime of the best-performance and best-lifetime single granularity schemes, respectively.