The page size of NAND flash continuously grows as the manufacturing process advances. While larger pages can reduce the cost per bit and improve the throughput of NAND flash, it may waste the storage space and data transfer time, causing more frequent garbage collections when serving small write requests. The main methods solving the mismatch problem between the request size and the write unit are write buffer cache and flash page reprogramming. However, multi-level cell (MLC) chips impose additional constraints on page programming so reprogramming MLC pages is prohibited. We proposed a multiple subpage writing flash translation layer (MSPW-FTL) for MLC by exploiting single-level cell (SLC)/MLC dual mode and flash page reprogramming feature. By converting MLC mode blocks to SLC mode blocks, we store small data in subpages of the SLC mode block. Moreover, we proposed three management methods to improve system efficiency: 1) two-level mapping to serve requests of different sizes; 2) an allocation strategy determines how the subpages of different logical pages are mapped to physical pages; and 3) a data management module to deal with the data fragmentation caused by the subpage granularity allocation. We compared MSPW-FTL with some related state-of-the-art FTLs under different types of workloads. Experimental results show that in average, MSPW-FTL reduces the I/O response time by 57.2%, the write amplification by 52.1%, and the number of erasures by 34.1%.

中文翻译：

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通过利用双模式操作在 MLC 中实现多子页写入 FTL

随着制造工艺的进步，NAND 闪存的页面大小不断增长。虽然较大的页面可以降低每位成本并提高 NAND 闪存的吞吐量，但它可能会浪费存储空间和数据传输时间，在处理小写请求时导致更频繁的垃圾收集。解决请求大小和写单元不匹配问题的主要方法是写缓冲区缓存和闪存页面重编程。然而，多层单元 (MLC) 芯片对页面编程施加了额外的限制，因此禁止重新编程 MLC 页面。我们通过利用单级单元 (SLC)/MLC 双模式和闪存页面重新编程功能，为 MLC 提出了多子页面写入闪存转换层 (MSPW-FTL)。通过将 MLC 模式块转换为 SLC 模式块，我们将小数据存储在 SLC 模式块的子页面中。此外，我们提出了三种管理方法来提高系统效率：1）两级映射来服务不同规模的请求；2）分配策略决定了不同逻辑页的子页如何映射到物理页；3)数据管理模块，用于处理子页面粒度分配造成的数据碎片。我们在不同类型的工作负载下将 MSPW-FTL 与一些相关的最先进 FTL 进行了比较。实验结果表明，MSPW-FTL平均降低了57.2%的I/O响应时间、52.1%的写放大和34.1%的擦除次数。2）分配策略决定了不同逻辑页的子页如何映射到物理页；3)数据管理模块，用于处理子页面粒度分配造成的数据碎片。我们在不同类型的工作负载下将 MSPW-FTL 与一些相关的最先进 FTL 进行了比较。实验结果表明，MSPW-FTL平均降低了57.2%的I/O响应时间、52.1%的写放大和34.1%的擦除次数。2）分配策略决定了不同逻辑页的子页如何映射到物理页；3)数据管理模块，用于处理子页面粒度分配造成的数据碎片。我们在不同类型的工作负载下将 MSPW-FTL 与一些相关的最先进 FTL 进行了比较。实验结果表明，MSPW-FTL平均降低了57.2%的I/O响应时间、52.1%的写放大和34.1%的擦除次数。