From btrfs Wiki

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.

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

linux v5.8 (Aug 2020)

Hilights: speedup dead root detection during orphan cleanup send will emit file capabilities after chown

Core changes: improved global block reserve utilization direct io cleanups and fixes refactored block group reading code lots of other core changes see the pull request



btrfs-progs v5.7 (Jul 2020)

mkfs: new option to enable features otherwise enabled at runtime, now implemented for quotas, 'mkfs.btrfs -R quota' fix space accounting for small image, DUP and --rootdir option -A removed

check: detect ranges with overlapping csum items

fi usage: report correct numbers when plain RAID56 profiles are used

convert: ensure the data chunks size never exceed device size

libbtrfsutil: update documentation regarding subvolume deletion

build: support libkcapi as implementation backend for cryptographic primitives

core: global options for verbosity (-v, -q), subcommands -v or -q are aliases and will continue to work but are considered deprecated, current command output is preserved to keep scripts working

other: block group code cleanups build warning fixes more files moved to kernel-shared btrfs-debugfs ported to python 3 documentation updates new tests



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:

Manual pages

Manual pages generated from git (complete list): btrfs — main administration tool mkfs.btrfs — creating the filesystem btrfs check — repairing file systems btrfs-convert — tool to convert in-place from ext2/3/4 filesystems to btrfs. For a greater detail of how the algorithm works, please see the Conversion from Ext3 page.



Original wiki documentation (obsolete, will be removed) restore and find-root — utilities to find and restore data from an unmountable filesystem



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

Btrfs design — design notes (possibly out of date in places)

Multiple Device Support — design notes

ENOSPC — Current ENOSPC design issues

Design_notes_on_Send/Receive — notes from initial impelentation, protocol V2 updates draft

Qgroups status quo - notes on some qgroups observations/pain points

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 User notes on dedupe — User/tester notes for using in-band deduplication feature



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.