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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

For feature status and stability, please refer to the Status page. The filesystem disk format is stable; this means that 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, xxhash, sha256, blake2b)
  • Compression (ZLIB, LZO, ZSTD), heuristics
  • 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 ext2/3/4 and reiserfs 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)
  • Swapfile support
  • Tree-checker, post-read and pre-write metadata verification

Features by kernel version

As part of the changelog you can also review

Features Currently in Development or Planned for Future Implementation

  • SMR (zoned block device) support
  • DAX/persistent memory support
  • The file/directory -level encryption support (fscrypt)

News

btrfs-progs v5.10 (Jan 2021)

  • scrub status:
    • print percentage of progress
    • add size unit options
  • fi usage: also print free space from statfs
  • convert: copy full 64 bit timestamp from ext4 if availalble
  • check:
    • add ability to repair extent item generation
    • new option to remove leftovers from inode number cache (-o inode_cache)
  • check for already running exclusive operation (balance, device add/...) when starting one
  • preliminary json output support for 'device stats'
  • fixes:
    • subvolume set-default: id 0 correctly falls back to toplevel
    • receive: align internal buffer to allow fast CRC calculation
    • logical-resolve: distinguish -o subvol and bind mounts
  • build: new dependency libmount
  • other
    • doc fixes and updates
    • new tests
    • ci on gitlab temporarily disabled
    • debugging output enhancements

linux v5.10 (Dec 2020)

  • hilights
    • performance improvements in fsync (dbench workload: higher throughput, lower latency)
    • sysfs exports current exclusive operataion (balance, resize, device add/del/...)
    • sysfs exports supported send stream version
  • core
    • direct io uses iomap infrastructure (no more struct buffer_head)
    • space reservations for data now use ticket infrastructure
    • cleanups, refactoring, preparatory work
    • error handling improvements
    • fixes

linux v5.9 (Oct 2020)

  • hilights
    • add mount option rescue to unify options for various recovery tasks on a mounted filesystems
    • mount option inode_cache is deprecated and will be removed in 5.11
    • removed deprecated options alloc_start and subvolrootid
    • sysfs exports information about qgroups and relations
    • FS_INFO ioctl exports more information from the filesystem (notably type of checksum)
    • running balance detects Ctrl-C too
    • performance improvements in fsync
    • mount-time prefetch of chunk tree

Changelog

Read about past releases in the separate Changelog page

Documentation

Guides and usage information

External Btrfs Documentation / Guides

Links to Btrfs documentation of various Linux distributions:

Project information/Contact

Manual pages

  • Original wiki documentation (obsolete, will be removed)

Developer documentation

  • 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

Btrfs source repositories describes purpose and contents, here are a few quick links:

Wiki accounts, editing

The wiki contributions are welcome! Please create an account and wait for approval (this is a necessary spam protection and we cannot remove it). You can try to catch some of the wiki admins on IRC (or ping user 'kdave' in a query) to expedite the account creation.

The registration requires full name for account but it's not mandatory from our perspective. The wiki User and User talk pages are created automatically but removed after account is approved. If you want to use the pages, create them manually, they won't be deleted.

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

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