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Read about past releases in the [[Changelog]]
Read about past releases in the [[Changelog]]
== Documentation ==
== Documentation ==
Revision as of 22:39, 2 September 2015
Btrfs is a new copy on write (CoW) filesystem for Linux aimed at implementing advanced features while 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.
The filesystem disk format is no longer unstable, and it's not expected to change unless there are strong reasons to do so. If there is a format change, file systems with a unchanged format will continue to be mountable and usable by newer kernels.
The Btrfs code base is under heavy development. Every effort is being made to keep it stable and fast. Due to the fast development speed, the state of development of the filesystem improves noticeably with every new Linux version, so it's recommended to run the most modern kernel possible.
For benchmarks, it's recommended to test the latest stable Linux version, and not any older. If possible, it's also recommendable to test the latest Linux development version. Also, it's recommended to test the different options, f.e. different compression options.
Newly added features may need a few releases to stabilize.
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.
The main Btrfs features available at the moment include:
- 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, Striping with Single and Dual Parity implementations
- 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 fixing errors on 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)
Additional features in development, or planned, include:
- Fast offline filesystem check
- Online filesystem check
- Object-level mirroring and striping
- Alternative checksum algorithms
- In-band deduplication (happens during writes)
- Other compression methods (snappy, LZ4)
- Hot data tracking and moving to faster devices (currently being pushed as a generic feature available through VFS)
Linux v4.2 (Aug 2015)
- transaction abort now reports the caller, not the helper function
- INO_LOOKUP ioctl: unprivileged if used to just get the rootid (aka. subvolume id)
- unified subvol= and subvolid= mounting, show the mounted subvol in mount options; also, /proc/self/mountinfo now always correctly shows the mounted subvolume
- reworked internal qgroup logic
- send: use received_uuid of parent during send
- sysfs: preparatory works for exporting more stats about devices
- deduplication on the same inode works
- deduplication does not change mtime/ctime
- in send: cloning, renames, orphans,
- few more ENOSPC fixes in case of block group creation/removal
- fix hang during inode eviction due to concurrent readahead
- EXTENT_SAME ioctl: handle unaligned length
- more fixes around automatic block group removal
- deadlock with EXTENT_SAME and readahead
- for feature NO_HOLES: fsync, truncate
btrfs-progs 4.1.2 (Jul 2015)
- urgent bugfix: mkfs creates invalid filesystem
In coreutils 8.24
Read about past releases in the Changelog
Guides and usage information
- Getting started — first steps, distributions with btrfs support
- FAQ — About the btrfs project and filesystem
- UseCases — Recipes for how to do stuff with btrfs
- SysadminGuide — A more in-depth guide to btrfs's concepts and a bit of its internals, to answer all those "but what is a subvolume?" kind of questions.
- Multiple devices – A guide to the RAID features of Btrfs
- Conversion from Ext3 and Ext4
- Problem FAQ — Commonly-encountered problems and solutions.
- Gotchas — lists known bugs and issues, but not necessarily solutions.
External Btrfs Documentation / Guides
Links to Btrfs documentation of various Linux distributions:
- "The Btrfs File System" chapter in the Oracle Linux 6 Administrator's Solutions Guide
- Oracle Linux Hands-on lab - Storage Management with Btrfs
- Major File Systems in Linux chapter in the SLES 11 Storage Administration Guide
- Btrfs chapter in the Red Hat Enterprise Linux 6 Storage Administration Guide
- Btrfs Wiki page on the Ubuntu Community Help Wiki
- Btrfs Wiki page on the Arch Linux Wiki
- BTRFS Fun Wiki page on the Funtoo Wiki
- Marc MERLIN's Btrfs talk at Linuxcon JP 2014 which gives an overview of Btrfs, best practices, and its more interesting features.
- Changelog — history of changes in linux kernel wrt btrfs
- Contact information:
- Project ideas
- Cleanup ideas
- Userspace tools projects
Using the built-in tools
- Manual pages generated from git (complete list):
- Original wiki documenation (obsolete, will be removed)
- restore and find-root — utilities to find and restore data from an unmountable filesystem
- Developer's FAQ — hints and answers for contributors and developers
- 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
Source code download
- Btrfs source repositories
- Gitweb source viewer of the main kernel repository
- Gitweb source viewer of the userspace tools repository
Articles, presentations, podcasts
- Video: NYLUG Presents: Chris Mason on Btrfs (May 14th 2015) by Chris Mason at the 192nd meeting of the NYLUG
- Video: Why you should consider using btrfs ... like Google does. by Marc Merlin at linux.conf.au 2015. talk slides
- Article: Bitrot and atomic COWs: Inside “next-gen” filesystems (ars technica, 2014/01)
- Article: Btrfs: Subvolumes and snapshots (LWN.net, 2014/01)
- Article: Btrfs: Working with multiple devices (LWN.net, 2013/12)
- Article: Btrfs: Getting started (LWN.net, 2013/12)
- Article: Btrfs hands on: An extremely cool file system (ZDNet, 2013/11)
- Technical report: Visualizating Block IO Workloads. Section six shows a visual comparison of the IO patterns for BTRFS, XFS, and EXT4. Submitted to ACM Transactions on Storage, November 2013.
- Paper: BTRFS: The Linux B-Tree Filesystem describing the overall concepts and architecture, appeared in ACM Transactions on Storage, August 2013. Includes a detailed comparison with ZFS. There is a free ACM authorized link, from O. Rodeh's  page. Otherwise, you need a subscription for the ACM library.
- Article: A Beginner's Guide To Btrfs (2012-11-26)
- Article: How I Use the Advanced Capabilities of Btrfs by Margaret Bierman with Lenz Grimmer (2012-08-11)
- Article: How I Got Started with the Btrfs File System for Oracle Linux by Margaret Bierman with Lenz Grimmer (2012-07-11)
- Article: Btrfs Fun Wiki page on funtoo.org (2012-05)
- Video: Btrfs Filesystem: Status and New Features by Chris Mason at the 2012 Linux Foundation Collaboration Summit (2012-04-05)
- Article Btrfs - The Swiss Army Knife Of Storage by Josef Bacik (2012-02)
- Video: I Can't Believe This is Butter! A tour of btrfs by Avi Miller at linux.conf.au (2012-01-18)
- Article: A btrfs update at LinuxCon Europe on lwn.net (2011-11-02)
- Podcast: Podcast with Chris Mason: Btrfs overview and status update (2011-07-13)
- 2012-10 BTRFS, mount options and virtual machines: an in-depth look (Ilsistemista.net)
- 2012-06 BTRFS EXT3 EXT4 XFS and KVM virtual machine: a host-side filesystem comparison (Ilsistemista.net)
- 2012-06 BTRFS vs EXT3 vs EXT4 vs XFS performance on Fedora 17 (Ilsistemista.net)
- 2012-05 XFS, Btrfs, EXT4 Battle It Out On Linux 3.4 (Phoronix.com)
- 2012-05 Ext4, XFS and Btrfs benchmark redux
- 2012-03 Testing Out The Btrfs Mount Options On Linux 3.2 (Phoronix.com)
- 2012-03 Ubuntu 12.04 LTS - Benchmarking All The Linux File-Systems (Phoronix.com)
Links to old or obsolete documentation, articles. Kept for historical reasons. Stuff that's more than 3 years old.
Articles, presentations, podcasts
- Video: The Story So Far by Josef Bacik at LinuxCon Brazil (2010-08-31)
- Article: Linux.com Weekend Project: Get Started with Btrfs (2010-10-15)
- Webcast: State of "Btrfs" File System for Linux by Chris Mason (2010-08-26) [email registration and flash required]
- Article: Valerie Aurora: A short history of btrfs (2009-07-22)
- 2011-12 Btrfs Performance Analysis
- 2011-11 Testing The "Pretty Beefy" Btrfs Changes In Linux 3.2 (Phoronix.com)
- 2011-10 EXT3 vs EXT4 vs XFS vs BTRFS - filesystems comparison on Linux kernel 3.0.0 (Ilsistemista.net)
- 2011-09 Testing EXT4 & Btrfs On A Serial ATA 3.0 SSD (Phoronix.com)
- 2011-05 Linux 2.6.39: XFS Speeds-Up, EXT4 & Btrfs Unchanged (Phoronix.com)
- 2011-03 Btrfs LZO Compression Performance (Phoronix.com)
- 2010-12 Benchmarks Of The Btrfs Space Cache Option (Phoronix.com) Comparing the performance of Btrfs using the default mount options, using the space_cache mount option, using the compress mount option for Btrfs file compression, and lastly using both the space_cache and compression mount options to benefit from the free space caching and Zlib compression.
- 2010 SSD Linux benchmarking: Comparing filesystems and encryption method
- 2010-11 EXT3 vs EXT4 vs XFS vs BTRFS linux filesystems benchmark (Ilsistemista.net)
- 2010-11 Phoronix: The Linux 2.6.37 Kernel With EXT4 & Btrfs (Phoronix.com) Comparison between Btrfs and Ext4.
- 2010-10 One Billion Files Btrfs performs well in comparison to other filesystems, when there are a billion files in the filesystem.
- 2009-05 Phoronix Test With SSD Mode (Phoronix.com) This test show that btrfs is slower with ssd option activated. Ssd code has been updated during 2.6.30-rc and is expected to be faster.
- 2009-04 Phoronix Performance Test on Fedora 11 Preview (Phoronix.com) The phoronix workload is mostly CPU based, but they do have a few filesystem benchmarks. Btrfs performs well, but you can see the checksumming and metadata duplication show up on their single disk streaming write workload. dbench in general measures lots of different caching effects, and is not a great measure of everyday performance.
- 2008-10 Btrfs performance analysis by Steven Pratt and IBM The benchmarks from IBM demonstrate some bottlenecks we have in the extent recording on large workloads. We're working on fixes for these.
- 2008-04 Multi-device Benchmarks
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.