Sector log: Fine-grained storage management for solid state drives

Abstract

Although NAND flash-based solid-state drives (SSDs) excel magnetic disks in several aspects, the costs of write operations have been limiting their performance. The overheads of write operations are exacerbated by the fixed write unit (page) of flash memory, which is much larger than the sector size in magnetic disks. A write request from a file system, with a data size smaller than a page, becomes a full page write in SSDs. With the page size hidden internally in SSDs, file systems and applications may not be optimized to a fixed page size. Furthermore, to increase the density and bandwidth of flash memory, page sizes in SSDs have been increasing.

In this paper, we propose a sector-level data management mechanism for SSDs, called sector log. Sector log manages a small part of NAND flash memory in SSDs with sector-level mapping, and stores sub-page writes more efficiently than conventional SSDs. While current small DRAM buffers cannot absorb the working set of sub-page writes for certain applications, sector log uses ample persistent storage in flash memory. With the sector mapping mechanism, sector log provides a sector-accessible block device abstraction upon page-managed flash memory.