ON the upcoming 2.6.30 kernel is loaded with a number of new file systems — some of which are ext4 and btrfs. Another of the hot new file systems that is in 2.6.30 is NILFS. This file system is definitely one that you should test.

"NILFS is a log-structured file system supporting versioning of the entire file system and continuous snapshotting which allows users to even restore files mistakenly overwritten or destroyed just a few seconds ago."

NILFS is a new implementation of a log-structured file system (LFS) supporting continuous snapshotting. In addition to versioning capability of the entire file system, users can even restore files mistakenly overwritten or destroyed just a few seconds ago. Since NILFS can keep consistency like conventional LFS, it achieves quick recovery after system crashes.

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 online backup.

Snapshot administration is easy and quickly performable. NILFS will make snapshotting or versioning of the POSIX filesystem much familiar to you. The possible use of NILFS includes, versioning, tamper detection, SOX compliance logging, and so forth. It can serve as an alternative filesystem for Linux desktop environment, or as a basis of advanced storage appliances.

The current major version of NILFS is version 2, which is referred to as NILFS2. NILFS2 realizes online garbage collection that reclaims disk space with keeping multiple snapshots.

NILFS has the features listed below.

(1) Changes or additions to data are done without overwriting existing data. (2) When a series of data writes ( has been completed, a time-stamped snapshot is taken. (3) The snapshots can be taken continuously and automatically without disturbing the file service. (4) The B-tree is used for managing the file system to achieve efficient processing for large files or large numbers of files. (5) Ordinary personal computers can be used without adding special hardware.

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.
• Loadable kernel module; no recompilation of the kernel is required.

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