NILFS is a new implementation of a log-structured file system for the Linux 2.6 operating system. Conventional features of a log-structured file systems (LFS) are high write performance and fast recovery time. In addition, LFS prevents data write operations from overwriting the disk blocks, thereby minimizing the damage to file data and system consistency on hardware failure. Furthermore, LFS writes data and meta-data in the correct order which helps ensuring consistency in the entire file system. LFS can instantaneously create file system snapshots and check the file system speedy. We implemented ``NILFS'' using modern technology: For example, the file and inode blocks are managed by a B-tree structure, internal data are processed in 64 bit wide word size. The B-tree structure enables ``NILFS'' to create and store huge files.