NAND闪存文件系统YAFFS的研究

研究了NAND文件系统YAFFS的数据存储结构、文件操作、加载、损耗平衡、垃圾回收、读写效率等问题.YAFFS以含有元数据的页为更新单位,相应设计的Tnode树结构能较快地索引数据,文件操作性能较好,加载时扫描OOB区重建文件系统的索引和结构,而YAFFS2的改进使加载大大加快.YAFFS的不覆写更新和块分配策略,保证了损耗平衡,但是线性复杂度的垃圾回收算法和大粒度的锁机制,不利于读写有时限的系统.通过性能测试发现,YAFFS加载和损耗平衡性能较好,写性能随空间的减少而减少,读性能连续文件和不连续文件基本相同.但YAFFS与MTD驱动层的兼容性不好,使用和测试也没JFFS2广泛,需进一步完善.

Research on NAND flash file system YAFFS

The NAND file system YAFFS is researched,including the data storage structure,file operation,file system mount,wear levelling,garbage collection,reading/writeing efficiency.We found that YAFFS update unit is page with meta data.File data is indexed fast by Tnode tree with high the file operation efficiency.Initialization only scans the OOB area to rebuild the file sytsem index structure.The YAFFS2 speeds up the initialization greatly.The wear levelling is guaranteed by out place update and block allocation algorithm,but coarse grained lock method and garbage collection algorithm are not suitable for real time system.The stress test showns that YAFFS initialization and wear levelling is good.Writing speed reduces low with the reading of blank space,the read speed of continuous and discontinuous file is almost same.YAFFS is not compatible with MTD layer well,and not widely used like JFFS2,which needs further improvement.