Compound Mapping and Filter Algorithm for Hybrid SSD Structure

Abstract

With the recent development of byte-unit non-volatile random access memory (RAM), various methods utilizing quad level cell (QLC) not-AND (NAND) flash memory with non-volatile RAM have been proposed. However, tests have shown that these hybrid structures lead to a reduction in the performance of a hybrid solid state disk (SSD) owing to issues regarding space efficiency. This study proposes a compound address method and filter algorithm suitable for the next generation of NAND flash, called hybrid storage media, where QLCs and phase-change memory (PCM) are used together. The filter-mapping algorithm includes a management method that stores data in phase-change memory or flash memory according to the next command, which is accessed when a write command that is half or less than half a page in length is received from the file system. Tests have shown that the compound mapping and filter algorithm reduces the wasted pages by more than half and the number of merge operations is also significantly decreased. This leads to a decrease in the number of delete operations and improves the overall processing speed of the hardware.