Research Of Flash File System Based On Large Capacity NAND Flash Memory

Flash memory is a non-volatile storage device which still holds the data when power off. It has been widely used in various portable and embedded devices,such as PDAs, smart phones,digital cameras,MP3,MP4 and so on. As the development of embedded systems and mobile computing technology, there's an ever-increasing amount of data to be generated and stored. On the other hand, as a result of the improvement of flash memory manufacturing technology, the capacity of flash memory is expanding and the performance vs price ratio hasbeen enhanced. Somehow, the flash file system plays an vital role in the performance of flash. Atpresent, the flash file system could be divided into two category which are traditional disk file system that runs on a flash translation layer and specific file system designed especially for flash memory. In the first method, file system manipulate the flash as a disk which undermine theperformance of flash memory. On the contrary, the latter one is intended specially for flash memory.In this paper, we did a thorough study of the current JFFS2 flash file system and analyze it'sadvantages and disadvantages. We found out the reason why JFFS2 does not work well on large capacity flash memorys which is JFFS2 does not keep indexing informations on flash device. The whole file system tree is built in RAM when JFFS2 mounting through scan the flash memory block by block which takes takes a lot of time and is unacceptable.We propose a newly designed flash file system which based on large capacity NANDflash——LFFS(Large Flash File System). LFFS file system keeps file indexing information onflash memory as well as a super block which leads to the fast mounting of LFFS. In the LFFS, flash memory is divided into several regions which has the same capacity as each other. A logic and physical region mapping table is maintained in RAM which solve the problems caused by garbage collection. LFFS performs as well as we expected in the experiment. Somehow, it still needs to be improved in many aspects, like system stability and safety, in the future we'll keep working on it.