FlashLight: A Lightweight Flash File System for Embedded Systems

Abstract

A very promising approach for using NAND flash memory as a storage medium is a flash file system. In order to design a higher-performance flash file system, two issues should be considered carefully. One issue is the design of an efficient index structure that contains the locations of both files and data in the flash memory. For large-capacity storage, the index structure must be stored in the flash memory to realize low memory consumption; however, this may degrade the system performance. The other issue is the design of a novel garbage collection (GC) scheme that reclaims obsolete pages. This scheme can induce considerable additional read and write operations while identifying and migrating valid pages. In this article, we present a novel flash file system that has the following features: (i) a lightweight index structure that introduces the hybrid indexing scheme and intra-inode index logging, and (ii) an efficient GC scheme that adopts a dirty list with an on-demand GC approach as well as fine-grained data separation and erase-unit data allocation. We implemented FlashLight in a Linux OS with kernel version 2.6.21 on an embedded device. The experimental results obtained using several benchmark programs confirm that FlashLight improves the performance by up to 27.4% over UBIFS by alleviating index management and GC overheads by up to 33.8%.