3X Faster Speed Solid-State Drive with a Write Order Based Garbage Collection Scheme

Abstract

Solid-state drives (SSDs) are over-taking hard disk drives (HDDs) as high-volume storage in enterprise servers and data centers. However, SSDs write performance is limited due to their inability to overwrite in-place and need for garbage collection. To reduce the garbage collection (GC) overhead, a logical block address (LBA) scrambler has been proposed. However, the LBA scrambler has two issues: (1) SSD performance decreases with a hot and random workload, and (2) the table size of the LBA scrambler may become upto 0.85% of the SSD capacity. In this work, a write order (WO) based GC scheme is proposed to solve the first issue. The number of valid pages in the NAND flash block, the write order and erase count of the block are considered for victim block selection during GC. One of the key advantages of the WO GC is that it does not require a clock inside the SSD, which will not operate if the SSD power is off. Further, to solve the second issue of the large table size, a Sector Bundling scheme is proposed. From the results, SSD performance is improved 3×, and the LBA scrambler table size is reduced 16%.