(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 storages, 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 thesis, we present broadly two approaches in phase. As a first step with respect to the index structure, we propose a novel efficient metadata management scheme including $\It{embedding inode}$ and $\It{hybrid indexing}$ schemes for flash file systems. As a second step finally, we design a new flash file system, called $\It{FlashLight}$, which includes following features: ($\It{i}$) a lightweight index structure that introduces $\It{hybrid indexing scheme}$ and $\It{intra-inode index logging}$ and ($\It{ii}$) an efficient GC scheme that adopts a dirty list with an on-demand GC approach as well as fine-grained data separation and $\It{erase-unit data allocation}$. We implemented FlashLight in a Linux OS with kernel version 2.6.21 on an embedded device. With several benchmark programs, the experimental results confirm that FlashLight enhances the performance up to 27.4% over UBIFS by alleviating index management and GC overheads up to 33.8%.