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Btrfs is a modern copy on write (CoW) filesystem for Linux aimed at implementing advanced features while also focusing on fault tolerance, repair and easy administration. Jointly developed at multiple companies, Btrfs is licensed under the GPL and open for contribution from anyone. Not too many companies have said that they are using Btrfs in production, but we welcome those who can say so on the production users page.

Contents

Stability status

The filesystem disk format is stable; this means it is not expected to change unless there are very strong reasons to do so. If there is a format change, filesystems which implement the previous disk format will continue to be mountable and usable by newer kernels.

The Btrfs code base is under heavy development. Not only is every effort being made to ensure that it remains stable and fast but to make it more so with each and every commit. This rapid pace of development means that the filesystem improves noticeably with every new Linux release so it's highly recommended that users run the most modern kernel possible.

For benchmarks, it's recommended to test the latest stable Linux version, and not any older, as well as the latest Linux development versions. Also, it's recommended to test the various mount options such as different compression options.

As with all software, newly added features may need a few releases to stabilize.

If you find any behavior you suspect to be caused by a bug, performance issues, or have any questions about using Btrfs, please email the Btrfs mailing list (no subscription required). Please report bugs on Bugzilla.

Features

Linux has a wealth of filesystems from which to choose, but we are facing a number of challenges with scaling to the large storage subsystems that are becoming common in today's data centers. Filesystems need to scale in their ability to address and manage large storage, and also in their ability to detect, repair and tolerate errors in the data stored on disk.

Major Features Currently Implemented

  • Extent based file storage
  • 2^64 byte == 16 EiB maximum file size (practical limit is 8 EiB due to Linux VFS)
  • Space-efficient packing of small files
  • Space-efficient indexed directories
  • Dynamic inode allocation
  • Writable snapshots, read-only snapshots
  • Subvolumes (separate internal filesystem roots)
  • Checksums on data and metadata (crc32c)
  • Compression (zlib and LZO)
  • Integrated multiple device support
    • File Striping
    • File Mirroring
    • File Striping+Mirroring
    • Single and Dual Parity implementations (experimental, not production-ready)
  • SSD (flash storage) awareness (TRIM/Discard for reporting free blocks for reuse) and optimizations (e.g. avoiding unnecessary seek optimizations, sending writes in clusters, even if they are from unrelated files. This results in larger write operations and faster write throughput)
  • Efficient incremental backup
  • Background scrub process for finding and repairing errors of files with redundant copies
  • Online filesystem defragmentation
  • Offline filesystem check
  • In-place conversion of existing ext3/4 file systems
  • Seed devices. Create a (readonly) filesystem that acts as a template to seed other Btrfs filesystems. The original filesystem and devices are included as a readonly starting point for the new filesystem. Using copy on write, all modifications are stored on different devices; the original is unchanged.
  • Subvolume-aware quota support
  • Send/receive of subvolume changes
    • Efficient incremental filesystem mirroring
  • Batch, or out-of-band deduplication (happens after writes, not during)

Features Currently in Development or Planned for Future Implementation

  • Online filesystem check
  • Object-level mirroring and striping
  • Alternative checksum algorithms
  • In-band deduplication (happens during writes)
  • Other compression methods (LZ4)
  • Hot data tracking and moving to faster devices (currently being pushed as a generic feature available through VFS)

News

btrfs-progs 4.7 (Jul 2016)

  • convert: fix creating discontig extents
  • check: speed up traversing heavily reflinked extents within a file
  • check: verify qgroups of higher levels
  • check: repair can now fix wrong qgroup numbers
  • balance: new option to run in the background
  • defrag: default extent target size changed to 32MiB
  • du: silently skip non-btrfs dirs/files
  • documentation updates: btrfs(5), btrfs(8), balance, subvolume, scrub, filesystem, convert
  • bugfixes:
    • unaligned access (reported for sparc64) in raid56 parity calculations
    • use /bin/bash
    • other stability fixes and cleanups
  • more tests

Linux v4.7 (Jul 2016)

  • allow balancing to dup with multi-device
  • device deletion by id (additionally to by path)
  • renameat2: add support for RENAME_EXCHANGE and RENAME_WHITEOUT
  • enhanced selftests
  • more preparatory work for "blocksize < page size"
  • more validation checks of superblock (discovered by fuzzing)
  • advertise which crc32c implementation is being used at module load
  • fixed space report by df with mixed block groups
  • log replay fixes
  • device replace fixes

Read about past releases in the Changelog

Documentation

Guides and usage information

External Btrfs Documentation / Guides

Links to Btrfs documentation of various Linux distributions:

Project information/Contact

Using the built-in tools

  • Original wiki documentation (obsolete, will be removed)

Developer documentation

  • Developer's FAQ — hints and answers for contributors and developers, general information about patch formatting
  • Development notes — notes, hints, checklists for specific implementation tasks (eg. adding new ioctls)
  • Code documentation — trees, source files, sample code for manipulating trees
  • Data Structures — detailed on-disk data structures
  • Trees — detailed in-tree representation of files and directories
  • Original COW B-tree: Source code in C that implements the COW B-tree algorithms repository. Written by Ohad Rodeh at IBM Research in 2006, and released under a BSD license. This is a reference implementation, that works in user space.
  • Unmerged features
    • In-band (write) time deduplication

Source code download

Articles, presentations, podcasts


Historical resources

Links to old or obsolete documentation, articles. Kept for historical reasons. Stuff that's more than 3 years old.

Articles, presentations, podcasts

Benchmarks

Personal tools