NILFS

NILFS
Developer Nippon Telegraph and Telephone Cyber Space Laboratories
Full name New Implementation of a Log-structured File System
Introduced (Linux kernel)
Structures
File allocation B-tree
Limits
Max. file size 8 EiB
Other
Supported operating systems Linux kernel, (ReadOnly for NetBSD)

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

Important features

NILFS supports 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 to make consistent backups during use.

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 realized online garbage collection that reclaims disk space with keeping multiple snapshots.

Other NILFS features include:

Current Status

Supported Features

Additional features

OS Compatibility

Distribution Description
Debian NILFS is available in Debian 5.0 and later (lenny, squeeze, wheezy, and sid).
Ubuntu NILFS is available in Ubuntu 9.10 and later.
CentOS x86 and x86_64 for CentOS 5/6 are available on http://www.nilfs.org.
Fedora Building and installing nilfs-utils-2.1 is required in order to use NILFS in Fedora 14~16. For Fedora 15 and later, user also needs to build NILFS2 kernel module with explained steps.
openSUSE i586 and x86_64 for openSUSE and SUSE Linux Enterprise are available on openSUSE Build Service.
Gentoo NILFS is available in Gentoo Linux. A boot-cd with NILFS is available on PrRescue
Arch NILFS is available in Arch Linux.
Linux Mint NILFS is available in Linux Mint.
NixOS NILFS is available in NixOS.

A separate, BSD licensed implementation, currently with read-only support, is included in NetBSD.[3]

Description

Using a copy-on-write technique known as "nothing in life is free", 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.[4]

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

Relative Performance

In the January 2015 presentation SD cards and filesystems for embedded systems at Linux.conf.au, it was stated:[5]

“ If you've got a workload that's latency sensitive, you might want to use NILFS. If you've got one that's throughput sensitive, you might want to use F2FS. ”

—Peter Chubb

See also

References

External links