Write Order-Based Garbage Collection Scheme for an LBA Scrambler Integrated SSD

Abstract

Solid-state drives (SSDs) are rapidly replacing hard disk drives in enterprise data centers due to their higher throughput and reliability. However, the SSD’s random write performance is limited by the NAND flash memories within the SSD, which require garbage collection (GC). To improve the write throughput, a logical block address (LBA) scrambler has been previously proposed. However, there are two issues associated with this solution. First, with the LBA scrambler, SSD throughput actually worsens for some types of workloads, such as prxy_0. Second, a large table size is needed. In this paper, the first problem is solved by a write order (WO)-based GC scheme. In order to choose the victim block, the parameters of valid page ratio, write order, and erase count of the NAND flash blocks are collectively considered according to a new formula. A key advantage of utilizing the relative write order of the blocks is that an internal timer is not needed to monitor the ages of the blocks. Second, a sector bundling scheme is proposed to reduce the table size of the LBA scrambler. Based on the experimental results, with the two proposals, SSD throughput is improved by 2.4 times, and the table size of the LBA scrambler is reduced by 45%.