Sector-level log management to improve partial write performance in SSDs

Abstract

NAND flash-based solid-state drives (SSDs) excel the magnetic disks in fast random access latency, low energy consumption, and high reliability for mobile systems. However, flash memory allows only out-of-place writes with a much larger atomic write granularity than magnetic disks. Due to the restriction on write operations, any partial writes with data size smaller than the write granularity of flash memory cause the entire write unit to be written to a new location. Furthermore, the unit of write varies by flash chips and SSD designs, and is hidden internally. File systems and applications frequently sends partial write requests, incurring significantly more write operations than necessary. In this paper, we propose a sector-managed data log, called sector log, which uses part of NAND flash memory in SSDs. Sector log can manage the data region in sector unit, and thus, stores partial writes more efficiently than conventional SSDs. By reducing the negative effect of large page sizes in SSDs, sector log allows more flexible designs both for application programmers and SSD designers. In our trace-based evaluation, sector log can improve the throughput of an SSD by 126% for the TPC-C trace, with 8KB page size