Research And Implementation Of Embedded Filesystem Based On NAND Flash

With the prevalence of embedded system, Flash memory storage which has high capacity and low energy consumption has become the primary externed storage for embedded systems. In recent years, there is an increasing consumption of NAND Flash. With the increasing demand of NAND Flash, research on management of media is becoming a hot-spot in embedded field.Generally speaking, there are two kinds of methods applied to management of NAND Flash. One is to use a traditional block file-system to manage the flash, such as FAT32 or Ext2, because the NAND Flash can be simulated as a traditional R/W block device. The other one is to manage it via a specialized file-system, such as YAFFS. YAFFS is the only file-system designed especifically for NAND flash, which is under any operating system. YAFFS is thus designed to work within the constraints of, and exploit the features of, NAND flash to maximise performance.Although YAFFS already performs well, there is still a lot of room for improvement. At present, YAFFS has two disadvantages: too long mounting time and insufficient consideration for wear-leveling. Accounting to these two aspects, this paper proposes a new filesystem named FMNFS (Fast-Mounting NAND File-system).In order to shorten the mounting time, FMNFS changes the management of the data nodes. FMNFS stores the indices-information and data-information separately instead of putting them together. According to the contents of the spare-area, FMNFS only needs to scan a part of all blocks in NAND Flash when the file-system is mounted, that reduces the mounting time greatly.To implement the wear-leveling in FMNFS, two aspects should be considered. One is about the hot-data. The information of indexes is updated more frequently than the data, so the blocks stored indexes are destroyed more easily. The other one is about the cold-data that is large and read-only, so the blocks stored it have a longer lifespan than stored other data. The two wear-leveling algorithms are designed and implemented in this paper, and the results are validated by the experiments. The implementation of FMNFS is significant for reducing the mounting time and lengthening the lifespan of NAND Flash.