LBA Scrambler: A NAND Flash Aware Data Management Scheme for High-Performance Solid-State Drives

摘要

There is an increasing demand for the solid-state drive (SSD) due to its high speed, low power, and high reliability. However, random write intensive workload is not good for the SSD performance due to the inherent characteristics of the NAND flash memory. As the garbage collection (GC) causes the bottleneck of the SSD write performance due to the page-copy overhead, a NAND flash aware system is proposed to improve the SSD performance with a scheme called logical block address (LBA) scrambler. In the proposed scheme, new data are actively written to the fragmented pages in the next erase block. As a result, the number of valid pages inside the block is reduced when the block is recycled. Considering that there are NAND flash blocks full of valid pages in the proposed scheme, a skipping full block round robin (SFB_RR) GC policy is proposed, showing 0%–58% performance improvement compared with the RR GC policy. Furthermore, certain valid pages in the SSD have obsolete data due to the logical address remapping of the LBA scrambler, which cannot be invalidated by the conventional TRIM command, thus a SWEEP command is introduced. With the SWEEP command, maximum 12% additional SSD performance gain is obtained. From the experimental results, 35%–394% performance improvement, 27%–56% energy consumption reduction, and 25%–55% endurance enhancement are achieved by the proposed LBA scrambler scheme + SFB_RR GC policy + SWEEP command support, compared with the conventional SSD.