Recently, embedded systems equipped with flash memory storage, especially smartphones are very popular. Of course, flash based file systems adopted by these embedded systems have to provide high performance and high reliability. For example, YAFFS2(Yet Another Flash File System 2), a flash file system, utilizes the checkpoint mechanism in order to overcome the weak point of high initialization cost which the previous YAFFS suffers. However, if a sudden power failure happens or metadata generated by checkpoints during the unmount process is not completely written to flash memory, the YAFFS2 file system has a drawback of scanning the whole flash memory storage. In this paper, we propose a new metadata management scheme that improves the performance and the reliability of YAFFS2. Our scheme manages the metadata in main memory efficiently by dividing it into three types: cold, warm and hot metadata. Due to this metadata management, our scheme need not scan the whole flash memory although a power failure occurs or metadata generated by checkpoints does not exist in flash memory. Also, with regard to the unmount I/O cost, our scheme is more efficient than the previous scheme.