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(News: progs 5.14.2)
(News: remove progs 5.13.x)
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* more subpage support preparation
* more subpage support preparation
* for other changes see the [ pull request]
* for other changes see the [ pull request]
''' btrfs-progs v5.13.1 (Jul 2021) '''
* build: fix build on musl libc due to missing definition of NAME_MAX
* check:
** batch more work into one transaction when clearing v1 free space inodes
** detect directoris with wrong number of links
* libbtrfsutil: fix race between subvolume iterator and deletion
* mkfs: be more specific about supported profiles for zoned device
* documentation updates

Revision as of 15:07, 8 October 2021


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. Its main features and benefits are:

  • Snapshots which do not make the full copy of files
  • RAID - support for software-based RAID 0, RAID 1, RAID 10
  • Self-healing - checksums for data and metadata, automatic detection of silent data corruptions

Development of Btrfs started in 2007. Since that time, Btrfs is a part of the Linux kernel and is under active development.

Jointly developed at multiple companies, Btrfs is licensed under the GPL and open for contribution from anyone.

List of companies using btrfs in production.

Development and Issue Reporting

For feature status, please refer to the Status page.

The Btrfs code base is stable. However, new features are still under development. Every effort is made to ensure that it remains stable and fast at 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.

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.


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
  • Zoned mode support (SMR/ZBC/ZNS friendly allocation)

Features by kernel version

As part of the changelog you can also review

Features Currently in Development or Planned for Future Implementation

  • DAX/persistent memory support
  • The file/directory -level encryption support (fscrypt)
  • fsverity integration


Guides and usage information

External Btrfs Documentation / Guides

Links to Btrfs documentation of various Linux distributions:

Manual pages

  • Original wiki documentation (obsolete, will be removed)

Developer documentation

  • Development setup - how to build btrfs from sources and prepare a development environment
  • 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


IRC channel at

The #btrfs channel is at, bridge works (persistent room

btrfs-progs v5.14.2 (Oct 2021)

  • fixes
    • zoned mode
        • properly detect non-zoned devices in emulation mode
        • properly create quota tree
        • raid1c3/4 also excluded from unsupported profiles
    • use sysfs-based detection of device discard capability, fix mkfs-time trim for non-standard devices
    • mkfs: fix creation of populated filesystem with free space tree
    • detect multipath devices (needs libudev)
  • replace start: add option -K/--nodiscard, similar to what mkfs or device add has
  • dump-tree: print complete root_item
  • mkfs: add option --verbose
  • sb-mod: better help, no checksum calculation on read-only actions
  • subvol show:
    • print more information (regarding send and receive)
    • print warning if read-write subvolume has received_uuid set
  • property set:
    • add parameter -f to force changes
    • changing ro->rw switch now needs -f if subvolume has received_uuid set, (see documentation)
  • build: optional libudev (on by default)
  • other
    • remove deprecated support for CREATE_ASYNC bit for subvolume ioctl
    • CI updates
    • new and updated tests

linux v5.14 (Aug 2021)


  • new sysfs knob to limit scrub IO bandwidth per device
  • device stats are also available in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats
  • support cancellable resize and device delete ioctls
  • change how the empty value is interpreted when setting a property, so far we have only 'btrfs.compression' and we need to distinguish a reset to defaults and setting "do not compress", in general the empty value will always mean 'reset to defaults' for any other property, for compression it's either 'no' or 'none' to forbid compression
  • performance improvements (xattrs, truncate)
  • space handling improvements, preemptive flushing
  • more subpage support preparation
  • for other changes see the pull request

Source code download

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

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

Project information/Contact

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.

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