NAND flash-based solid-state drives (SSDs) have been widely used in consumer electronic products such as smartphones, digital video recorders, and laptops. The flash translation layer (FTL) is crucial to the performance of SSDs. In this article, an on-demand FTL, briefly as HDFTL, is proposed for hybrid SSDs built with SLC+MLC flash memory. HDFTL divides the SLC into data blocks and translation blocks and uses all MLC as data blocks. All mapping items are stored in the translation block of the SLC, and partial mapping items are loaded into the cached mapping table of the FTL as needed. The contributions of HDFTL are as follows: (1) Unify the address mapping method of SLC and MLC areas to simplify the FTL design of hybrid SSDs; (2) Split the cached mapping table into a hot-write mapping table and a normal mapping table and use time locality to solve hot-write identification problem in hybrid SSDs; (3) According to the relative wear rate of SLC and MLC areas, adaptively adjust the size of the hot-write mapping table and the normal mapping table. Experimental results show that the performance of HDFTL is better than that of the existing FTLs for hybrid SSDs.

中文翻译：

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HDFTL：混合固态驱动器的按需闪存转换层算法

基于NAND闪存的固态驱动器（SSD）已广泛用于智能手机，数字录像机和笔记本电脑等消费电子产品。闪存转换层（FTL）对于SSD的性能至关重要。在本文中，针对使用SLC + MLC闪存构建的混合SSD提出了按需FTL（简称HDFTL）。HDFTL将SLC分为数据块和转换块，并将所有MLC用作数据块。所有映射项都存储在SLC的转换块中，部分映射项会根据需要加载到FTL的缓存映射表中。HDFTL的贡献如下：（1）统一SLC和MLC区域的地址映射方法，以简化混合SSD的FTL设计；（2）将缓存的映射表分为热写映射表和普通映射表，并利用时间局部性解决混合SSD中的热写识别问题；（3）根据SLC和MLC区域的相对磨损率，自适应地调整热写映射表和法线映射表的大小。实验结果表明，HDFTL的性能优于现有的混合SSD的FTL。