The Research & Realization Of UBIFS Wear-Leveling In Linux-based Embedded System

NAND flash is facing three major challenges of garbage collection, wear-leveling and bad block handling because of the physical charactisitics of NAND flash. Therefore, NAND flash requires special memory storage technologies to solve these problems and the special flash filesystem is the most widely used solution in embedded system, which supports the log structured design and provides power protection, crash recovery mechanisim and garbage collection and so on.As the data stored in embedded system is mainly static,the dynamic data which is frequently updated will be focus on one area of the flash device that results in the uneven distribution of erase counter. Because the blocks containing dynamic data have more opportunities to be erased than the blocks containing static data, there is one region of flash device running out of their expect erase times which leads to the end of flash life and the static region is not fully used. This will result in great loss to user and is also not allowed in embedded system which requires low cost and low investment. We have to consider the wear-leveling mechanism especially in global domain to solve the problem of the limited life span in flash. As a new type of NAND flash file system, UBIFS implements the wear-leveling mechanism which is transparent to users. Therefore, it is meaningful to design and implement the optimization algorithm of UBIFS wear-leveling for an embedded system with static data.This paper analyzes the physical characteristics and challenges of NAND flash, and discusses different wear-leveling methods and serveral widely used wear-leveling algorithms.Then the UBIFS architecture and its wear-leveling mechanism are deeply analyzed, which also provide the basic knowlegment and reference for the optimization design. After studying the UBIFS source code and its concrete realization of wear-leveling, a detailed analysis of UBIFS tree structured management and UBI operations including the mapping mechanisim between LEB and PEB,provide the foundation of the optimation implemention. In this paper, the optimization algorithm is proposed with overall design architecture and the optimizated protection module is given in UBIFS wear-leveling subsystem, including the write requests collection function, the space assessment function and the data movement function. Test platform is performed to validate the design and realization of the optimized UBIFS wear-leveling.