NILFS

NILFS or NILFS2 (New Implementation of a Log-structured File System) is a log-structured file system implementation for the Linux kernel. It was developed by Nippon Telegraph and Telephone Corporation (NTT) CyberSpace Laboratories and a community from all over the world. NILFS was released under the terms of the GNU General Public License (GPL).

NILFS or NILFS2 (New Implementation of a Log-structured File System) is a log-structured file system implementation for the Linux kernel. It was developed by Nippon Telegraph and Telephone Corporation (NTT) CyberSpace Laboratories and a community from all over the world. NILFS was released under the terms of the GNU General Public License (GPL). ==Design== "NILFS is a log-structured file system, in that the storage medium is treated like a circular buffer and new blocks are always written to the end.[…]Log-structured file systems are often used for flash media since they will naturally perform wear-leveling;[…]NILFS emphasizes snapshots. The log-structured approach is a specific form of copy-on-write behavior, so it naturally lends itself to the creation of file system snapshots. The NILFS developers talk about the creation of "continuous snapshots" which can be used to recover from user-initiated file system problems[…]." Using a copy-on-write technique known as a log-structured file system, NILFS records all data in a continuous log-like format that is only appended to, never overwritten, an approach that is designed to reduce seek times, as well as minimize the kind of data loss that occurs after a crash with conventional file systems. For example, data loss occurs on ext3 file systems when the system crashes during a write operation. When the system reboots, the journal notes that the write did not complete, and any partial data writes are lost. Some file systems, like UFS-derived file systems used by the Solaris operating system and BSDs, provide a snapshot feature that prevents such data loss, but the snapshot configuration can be lengthy on large file systems. NILFS, in contrast, can "continuously and automatically [save] instantaneous states of the file system without interrupting service", according to NTT Labs. The "instantaneous states" that NILFS continuously saves can actually be mounted, read-only, at the same time that the actual file system is mounted read-write — a capability useful for data recovery after hardware failures and other system crashes. The "lscp" (list checkpoint) command of an interactive NILFS "inspect" utility is first used to find the checkpoint's address, in this case "2048": # inspect /dev/sda2 ... nilfs> listcp 1 6 Tue Jul 12 14:55:57 2005 MajorCP|LogiBegin|LogiEnd 2048 2352 Tue Jul 12 14:55:58 2005 MajorCP|LogiEnd ... nilfs> quit The checkpoint address is then used to mount the checkpoint: # mount -t nilfs -r -o cp=2048 /dev/sda2 /nilfs-cp # df Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda2 70332412 8044540 62283776 12% /nilfs /dev/sda2 70332412 8044540 62283776 12% /nilfs-cp ==Features== NILFS provides continuous snapshotting. In addition to the versioning capability of the entire file system, users can even restore files mistakenly overwritten or deleted at any recent time. Since NILFS can keep consistency like conventional LFS, it achieves quick recovery after system crashes. Continuous snapshotting is not provided by most file systems, including those supporting point-in-time snapshotting (e.g. Btrfs). NILFS creates a number of checkpoints every few seconds or per synchronous write basis (unless there is no change). Users can select significant versions among continuously created checkpoints, and can change them into snapshots which will be preserved until they are changed back to checkpoints. There is no limit on the number of snapshots until the volume gets full. Each snapshot is mountable as a read-only file system. It is mountable concurrently with a writable mount and other snapshots, and this feature is convenient for making consistent backups during use. Possible uses of NILFS include versioning, tamper detection, SOX compliance logging, data loss recovery. The current major version of NILFS is version 2, referred to as NILFS2. NILFS2 implements online garbage collection to reclaim disk space while keeping multiple snapshots. Other NILFS features include: B-tree based file and inode management. Immediate recovery after system crash. 64-bit data structures; support many files, large files and disks. 64-bit on-disk timestamps which are free of the year 2038 problem. ===Current status=== ===Issues=== As of 2023, NILFS lacks a dedicated consistency checking utility (fsck), and thus can't recover from severe errors that cause it to fail to find a valid checkpoint. ====Supported features==== Basic POSIX file system features Snapshots Automatically and continuously taken No limit on the number of snapshots until the volume gets full Mountable as read-only file systems Mountable concurrently with the writable mount (convenient to make consistent backups during use) Quick listing Background garbage collection (GC) Can maintain multiple snapshots Selectable GC Policy, which is given by a userland daemon. Quick crash recovery on-mount Read-ahead for meta data files as well as data files Block sizes smaller than page size (e.g. 1 KB or 2 KB) Online resizing (since Linux-3.x and nilfs-utils 2.1) Related utilities (by contribution of Jiro SEKIBA) grub2 util-linux (blkid, libblkid, uuid mount) udisks, palimpsest File system label (nilfs-tune) ==License== The NILFS2 file system utilities are made available under the GNU General Public License version 2, with the exception of the lib/nilfs libraries and their header files, which are made available under the GNU Lesser General Public License Version 2.1. ==References== ==External links== Manjaro tutorial NILFS: A filesystem designed to minimize the likelyhood [sic of data loss ]

Text derived from https://en.wikipedia.org/w/index.php?oldid=1326894465 under CC BY-SA 4.0; modifications have been made.