btrfs

Structures
Btrfs
Developer	Oracle Corporation
Full name	Btrfs
Introduced	Stable: Yet to be released Unstable: August 2008 (Linux)
Directory contents	B-tree
File allocation	extents
Limits
Max file size	16 EB
Max number of files	2⁶⁴
Max filename length	255 bytes
Max volume size	16 EB
Allowed characters in filenames	All bytes except NUL and '/'
Features
Attributes	POSIX
File system permissions	POSIX, ACL
Transparent encryption	No
Supported operating systems	Linux

Btrfs (B-tree FS or usually pronounced "Butter FS"^[1]^[2]) is a copy-on-write file system for Linux announced by Oracle in 2007.^[3] It was created as a response to the ZFS filesystem, in order to replace the ext3 file system while removing a number of its limitations, particularly with respect to file size, total file system size and filesystem check duration; it is also expected to implement modern filesystem features not supported by ext3, like writable snapshots, snapshots of snapshots, builtin RAID support, and subvolumes. In addition, Btrfs claims a "focus on fault tolerance, repair and easy administration."^[4]

As of August 2008^[update], Btrfs is still under heavy development and is only intended for testing. Btrfs v0.16 was released August 5, 2008, as free software under the GNU General Public License (GPL).^[5] Btrfs v1.0 (with finalized on-disk format) is scheduled to be released in late 2008.^[6] Theodore Ts'o, developer of ext3 and ext4 filesystems, said that Btrfs “has a number of the same design ideas that Reiser4 had”.

Chris Mason, Director of Linux Kernel Engineering at Oracle and the founder of Btrfs said that, "The main goal is to let it {Linux} scale for the storage that will be available. Scaling is not just about addressing the storage but also means being able to administer and to manage it with a clean interface that lets people see what's being used and makes it more reliable."^[7] Mason also noted that he expects the initial Btrfs merge with Linux to occur in the Linux 2.6.29 kernel.^[7]

1 Features
2 See also
3 References
4 External links

Features

Btrfs is still in heavy development and many basic features are still missing (like detecting when the disk is full, as of May 2008^[update]). It includes, or has plans for:^[8]

Space-efficient packing of small files and indexed directories
Dynamic inode allocation (no maximum number of files set at file system creation time)
Writable snapshots and snapshots of snapshots
Subvolumes (separate internal filesystem roots)
Object-level mirroring and striping
Checksums on data and metadata (for strong integrity assurance)
Compression
Copy-on-write logging for all data and metadata
Strong integration with device mapper for multiple device support, with several built in RAID algorithms
Online filesystem check and very fast offline filesystem check
Efficient incremental backup and file system mirroring
A filesystem can be upgraded from ext3fs to Btrfs
Solid-state drive (SSD) optimized mode (activated through mount option)
Online defragmentation

Although Btrfs has no native feature that would make it a distributed or networked filesystem by itself, Oracle is also implementing CRFS (Coherent Remote File System), a network filesystem protocol specifically designed and optimized for networked storage on Btrfs.

References

^ Valerie Henson. (2008-01-31). Chunkfs: Fast file system check and repair. Retrieved on 2008-02-05. Event occurs at 18m 49s. "It's called Butter FS or B-tree FS, but all the cool kids say Butter FS"
^ CRFS and POHMELFS [LWN.net]
^ Chris Mason (2007-06-12). "Btrfs: a copy on write, snapshotting FS". Linux Kernel Mailing List. Retrieved on 2007-07-11.
^ Chris Mason (2008-03-12). "Btrfs wiki Main Page". Retrieved on 2008-08-09.
^ Btrfs v0.16 released
^ http://btrfs.wiki.kernel.org/index.php/Development_timeline
^ ^a ^b Sean Michael Kerner (2008-10-30). "A Better File System For Linux". InternetNews.com. Retrieved on 2008-10-30.
^ Feature list from Jonathan Corbet (2007-06-19). "btrfs and NILFS". and Chris Mason (2007-06-12). "Btrfs: a copy on write, snapshotting FS". Linux Kernel Mailing List.