Main Page

From btrfs Wiki
(Difference between revisions)
Jump to: navigation, search
(News and Changelog: linux 5.6)
(link to RTD)
(113 intermediate revisions by 7 users not shown)
Line 1: Line 1:
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 [[Contributors|multiple companies]], Btrfs is licensed under the GPL and open for contribution from anyone.
+
__NOTOC__
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|production users]] page.
+
<!-- Welcome Block -->
 +
<div style="margin:0; margin-top:10px; margin-right:10px; border:1px solid #dfdfdf; padding:0 1em 1em 1em; align:right; ">
 +
[[File:Btrfs_logo_small.png|200px|left|btrfs]]
  
== Stability status ==
+
'''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:
  
'''For a feature status and stability please refer to the [[Status]] page.''' The filesystem [[On-disk_Format|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.
+
* '''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
  
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.
+
Development of Btrfs started in 2007. Since that time, Btrfs is a part of the Linux kernel and is under active development.
  
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.
+
Jointly developed by multiple companies (https://btrfs.readthedocs.io/en/latest/Contributors.htm, Btrfs is licensed under the GPL and open for contribution from anyone.
  
As with all software, newly added features may need a few releases to stabilize.
+
[[Production_Users|List of companies using btrfs in production]].
 +
</div>
 +
 
 +
{| width="100%"
 +
|-
 +
|style="vertical-align:top" |
 +
 
 +
<!-- Development and Issue Reporting Block -->
 +
<div style="margin:0; margin-top:10px; margin-right:10px; border:1px solid #dfdfdf; padding:0 1em 1em 1em; background-color:#dcf5ff; align:right;">
 +
== 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 [[Manpage/btrfs(5)#MOUNT_OPTIONS|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 [[Problem_FAQ#How_do_I_report_bugs_and_issues.3F|Bugzilla]].
 
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 [[Problem_FAQ#How_do_I_report_bugs_and_issues.3F|Bugzilla]].
 +
</div>
  
 +
<!-- Features Block -->
 +
<div style="margin:0; margin-top:10px; margin-right:10px; border:1px solid #dfdfdf; padding:0 1em 1em 1em; background-color:#F8F8FF; align:right;">
 
== Features ==
 
== Features ==
  
Line 21: Line 43:
 
* Extent based file storage
 
* Extent based file storage
 
* 2^64 byte == 16 EiB maximum file size (practical limit is 8 EiB due to Linux VFS)
 
* 2^64 byte == 16 EiB maximum file size (practical limit is 8 EiB due to Linux VFS)
* Space-efficient packing of small files
+
* [https://btrfs.readthedocs.io/en/latest/Inline-files.html Space-efficient packing of small files]
 
* Space-efficient indexed directories
 
* Space-efficient indexed directories
 
* Dynamic inode allocation
 
* Dynamic inode allocation
 
* Writable snapshots, read-only snapshots
 
* Writable snapshots, read-only snapshots
* Subvolumes (separate internal filesystem roots)
+
* [https://btrfs.readthedocs.io/en/latest/Subvolumes.html Subvolumes] (separate internal filesystem roots)
* Checksums on data and metadata (crc32c, xxhash, sha256, blake2b)
+
* [https://btrfs.readthedocs.io/en/latest/Checksumming.html Checksums on data and metadata] (crc32c, xxhash, sha256, blake2b)
* [[Compression]] (zlib, LZO, ZSTD), heuristics
+
* [https://btrfs.readthedocs.io/en/latest/Compression.html Compression] (ZLIB, LZO, ZSTD), heuristics
 
* Integrated [[Multiple_Device_Support|multiple device support]]
 
* Integrated [[Multiple_Device_Support|multiple device support]]
 
** File Striping
 
** File Striping
Line 33: Line 55:
 
** File Striping+Mirroring
 
** File Striping+Mirroring
 
** Single and Dual Parity implementations (experimental, not production-ready)
 
** 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)
+
* SSD (flash storage) awareness
* Efficient [[Incremental_Backup|incremental backup]]
+
** [https://btrfs.readthedocs.io/en/latest/Trim.html TRIM/Discard] for reporting free blocks for reuse
* Background scrub process for finding and repairing errors of files with redundant copies
+
** 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)
* Online filesystem defragmentation
+
* Background [https://btrfs.readthedocs.io/en/latest/Scrub.html scrub] process for finding and repairing errors of files with redundant copies
* [[btrfsck|Offline filesystem check]]
+
* Online filesystem [https://btrfs.readthedocs.io/en/latest/Defragmentation.html defragmentation]
 +
* [https://btrfs.readthedocs.io/en/latest/btrfs-check.html Offline filesystem check]
 
* In-place [[Conversion_from_Ext3|conversion]] of existing ext2/3/4 and reiserfs file systems
 
* In-place [[Conversion_from_Ext3|conversion]] of existing ext2/3/4 and reiserfs file systems
* [[Seed-device|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.
+
* [https://btrfs.readthedocs.io/en/latest/Seeding-device.html Seeding 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]]
+
* Subvolume-aware [https://btrfs.readthedocs.io/en/latest/Qgroups.html quota support]
* Send/receive of subvolume changes
+
* [https://btrfs.readthedocs.io/en/latest/Send-receive.html Send/receive] of subvolume changes, efficient incremental filesystem mirroring and [[Incremental_Backup|backup]]
** Efficient incremental filesystem mirroring
+
 
* Batch, or out-of-band [[deduplication]] (happens after writes, not during)
 
* Batch, or out-of-band [[deduplication]] (happens after writes, not during)
* Swapfile support
+
* [https://btrfs.readthedocs.io/en/latest/Swapfile.html Swapfile] support
* [[Tree-checker]] for extra robustness
+
* [https://btrfs.readthedocs.io/en/latest/Tree-checker.html Tree-checker], post-read and pre-write metadata verification
 +
* [[Zoned]] mode support (SMR/ZBC/ZNS friendly allocation)
 +
* fsverity integration
  
 
=== Features by kernel version ===
 
=== Features by kernel version ===
As part of the changelog you can also review
 
  
 
* [[Changelog#By_feature|features by kernel version]]
 
* [[Changelog#By_feature|features by kernel version]]
Line 54: Line 77:
 
=== Features Currently in Development or Planned for Future Implementation ===
 
=== Features Currently in Development or Planned for Future Implementation ===
  
* Online filesystem check
 
* Object-level mirroring and striping
 
* In-band deduplication (happens during writes)
 
* Hot data tracking and moving to faster devices (or provided on the generic VFS layer)
 
* SMR (zoned block device) support
 
 
* DAX/persistent memory support
 
* DAX/persistent memory support
 
* The file/directory -level encryption support (fscrypt)
 
* The file/directory -level encryption support (fscrypt)
  
== News and Changelog ==
+
=== Documentation ===
  
''' linux v5.6 (Mar 2020) '''
+
* https://btrfs.readthedocs.org or https://btrfs.rtfd.io
* Highlights:
+
* the #btrfs channel is at [https://libera.chat libera.chat], matrix.org bridge works (persistent room #btrfs:matrix.org).
** async discard
+
*** "mount -o discard=async" to enable it
+
*** freed extents are not discarded immediatelly, but grouped together and trimmed later, with IO rate limiting
+
*** the actual discard IO requests have been moved out of transaction commit to a worker thread, improving commit latency
+
*** IO rate and request size can be tuned by sysfs files, for now enabled only with CONFIG_BTRFS_DEBUG as we might need to add/delete the files and don't have a stable-ish ABI for general use, defaults are conservative
+
** export device state info in sysfs, eg. missing, writeable
+
** no discard of extents known to be untouched on disk (eg. after reservation)
+
** device stats reset is logged with process name and PID that called the ioctl
+
* Core changes:
+
** qgroup assign returns ENOTCONN when quotas not enabled, used to return EINVAL that was confusing
+
** device closing does not need to allocate memory anymore
+
** snapshot aware code got removed, disabled for years due to performance problems, reimplmentation will allow to select wheter defrag breaks or does not break COW on shared extents
+
** tree-checker:
+
*** check leaf chunk item size, cross check against number of stripes
+
*** verify location keys for DIR_ITEM, DIR_INDEX and XATTR items
+
*** new self test for physical -> logical mapping code, used for super block range exclusion
+
* Fixes:
+
** fix missing hole after hole punching and fsync when using NO_HOLES
+
** writeback: range cyclic mode could miss some dirty pages and lead to OOM
+
** two more corner cases for metadata_uuid change after power loss during the change
+
** fix infinite loop during fsync after mix of rename operations
+
* see [https://git.kernel.org/linus/81a046b18b331ed6192e6fd9ff6d12a1f18058cf pull request]
+
  
''' Notable fixes (Feb 2020) '''
+
</div>
* fix for <tt>df</tt> (statfs) reporting 0 after heavy metadata operation like balance
+
** 5.5.2, 5.4.18
+
  
''' btrfs-progs v5.4.1 (Jan 2020) '''
+
<!-- Documentation Block -->
* build: fix docbook5 build                                                                                                                                                                               
+
<div style="margin:0; margin-top:10px; margin-right:10px; border:1px solid #dfdfdf; padding:0 1em 1em 1em; background-color:#fffff0; align:right; ">
* check: do extra verification of extent items, inode items and chunks                                                                                                                                     
+
* qgroup: return ENOTCONN if quotas not running (needs updated kernel)                                                                                                                                     
+
* other: various test fixups
+
 
+
Read about past releases in the [[Changelog]]
+
* [[Changelog#By_feature|features by kernel version]]
+
* [[Changelog#By_version_.28linux_kernel.29|kernel changes]]
+
* [[Changelog#By_version_.28btrfs-progs.29|btrfs-progs]]
+
  
 
== Documentation ==
 
== Documentation ==
Line 117: Line 103:
 
* [[Problem FAQ]] — Commonly-encountered problems and solutions.
 
* [[Problem FAQ]] — Commonly-encountered problems and solutions.
 
** [[Gotchas]] — lists known bugs and issues, but not necessarily solutions.
 
** [[Gotchas]] — lists known bugs and issues, but not necessarily solutions.
 
=== External Btrfs Documentation / Guides ===
 
 
Links to Btrfs documentation of various Linux distributions:
 
 
* "[https://docs.oracle.com/cd/E37670_01/E37355/html/ol_btrfs.html The Btrfs File System]" chapter in the [https://docs.oracle.com/cd/E37670_01/E37355/html/index.html Oracle Linux 6 Administrator's Solutions Guide]
 
* Oracle Linux [https://wikis.oracle.com/display/oraclelinux/Hands-on+lab+-+Storage+Management+with+Btrfs Hands-on lab - Storage Management with Btrfs]
 
* [https://www.suse.com/documentation/sles11/stor_admin/data/sec_filesystems_major.html Major File Systems in Linux] chapter in the [https://www.suse.com/documentation/sles11/stor_admin/data/bookinfo.html SLES 11 Storage Administration Guide]
 
* [https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/ch-btrfs.html Btrfs] chapter in the [https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/ Red Hat Enterprise Linux 6 Storage Administration Guide]
 
* [https://help.ubuntu.com/community/btrfs Btrfs Wiki page] on the [https://help.ubuntu.com/community Ubuntu Community Help Wiki]
 
* [https://wiki.archlinux.org/index.php/Btrfs Btrfs Wiki page] on the [https://wiki.archlinux.org/ Arch Linux Wiki]
 
* [http://www.funtoo.org/BTRFS_Fun BTRFS Fun Wiki page] on the [http://www.funtoo.org/ Funtoo Wiki]
 
* [http://marc.merlins.org/perso/btrfs/post_2014-05-21_My-Btrfs-Talk-at-Linuxcon-JP-2014.html Marc MERLIN's Btrfs talk at Linuxcon JP 2014] which gives an overview of Btrfs, best practices, and its more interesting features.
 
 
=== Project information/Contact ===
 
 
* [[Changelog]] — history of changes in linux kernel wrt btrfs
 
** [[Changelog#By_feature | features added by release]]
 
* [[Contributors#Statistics_for_5.x_series|Development statistics]] — contributors, commits, lines
 
* [[Glossary]]
 
* Contact information:
 
** [[Btrfs mailing list]]
 
** [http://en.wikipedia.org/wiki/Internet_Relay_Chat IRC] on freenode.net in the channel [irc://irc.freenode.net:6667/btrfs #btrfs]
 
** Reporting bugs:
 
*** for kernel code see [[Problem_FAQ#How_do_I_report_bugs_and_issues.3F | the Bugzilla FAQ]], quick tip: use product ''File System'' and component ''btrfs''.
 
*** for btrfs-progs it's either bugzilla or [https://github.com/kdave/btrfs-progs/issues/ github issues]
 
*** for read-only documentation exported on wiki eg. manual pages as [https://github.com/kdave/btrfs-progs/issues/ github issues]
 
* [[Project ideas]]
 
* [[Project_ideas#Cleanup_projects|Cleanup ideas]]
 
* [[Project_ideas#Userspace_tools_projects|Userspace tools projects]]
 
  
 
=== Manual pages ===
 
=== Manual pages ===
  
* Manual pages generated from git ([[:Category:Manpage|complete list]]):
+
* Manual pages generated from git ([https://btrfs.readthedocs.io/en/latest/man-index.html complete list]):
** [[Manpage/btrfs|btrfs]] — main administration tool
+
** [https://btrfs.readthedocs.io/en/latest/btrfs.html btrfs] — main administration tool
** [[Manpage/mkfs.btrfs|mkfs.btrfs]] — creating the filesystem
+
** [https://btrfs.readthedocs.io/en/latest/mkfs.btrfs.html mkfs.btrfs] — creating the filesystem
** [[Manpage/btrfs-check|btrfs check]] — repairing file systems
+
** [https://btrfs.readthedocs.io/en/latest/btrfs-check.html btrfs check] — repairing file systems
** [[Manpage/btrfs-convert|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.
+
** [https://btrfs.readthedocs.io/en/latest/btrfs-convert.html 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)
 
* Original wiki documentation (obsolete, will be removed)
Line 161: Line 117:
 
=== Developer documentation ===
 
=== Developer documentation ===
  
 +
* [[Development setup]] - how to build btrfs from sources and prepare a development environment
 +
 +
* [https://github.com/btrfs/btrfs-dev-docs Developer documentation on Github] - collection of documents describing internals of BTRFS
 
* [[Developer's FAQ]] — hints and answers for contributors and developers, general information about patch formatting
 
* [[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)
 
* [[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
 
* [[Data Structures]] — detailed on-disk data structures
 +
* [[On-disk_Format | On-disk Format]] - Details of data structures written on disk
 
* [[Trees]] — detailed in-tree representation of files and directories
 
* [[Trees]] — detailed in-tree representation of files and directories
  
 
* [[Btrfs design]] — design notes (possibly out of date in places)
 
* [[Btrfs design]] — design notes (possibly out of date in places)
 
* [[Multiple Device Support]] — design notes
 
* [[Multiple Device Support]] — design notes
* [[ENOSPC]] — Current ENOSPC design issues
 
 
* [[Design_notes_on_Send/Receive]] — notes from initial impelentation, protocol V2 updates draft
 
* [[Design_notes_on_Send/Receive]] — notes from initial impelentation, protocol V2 updates draft
 
* [[Qgroups status quo]] - notes on some qgroups observations/pain points
 
* [[Qgroups status quo]] - notes on some qgroups observations/pain points
Line 183: Line 141:
 
** In-band (write) time deduplication
 
** In-band (write) time deduplication
 
*** [[User notes on dedupe]] — User/tester notes for using in-band deduplication feature
 
*** [[User notes on dedupe]] — User/tester notes for using in-band deduplication feature
 +
</div>
  
==== Source code download ====
+
| width="50%" style="vertical-align:top" |
  
* [[Btrfs source repositories]]
+
<!-- News Block -->
* [http://git.kernel.org/?p=linux/kernel/git/mason/linux-btrfs.git;a=tree;f=fs/btrfs;hb=HEAD Gitweb source viewer] of the main kernel repository
+
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#f0e0d0; align:left;">
* [https://git.kernel.org/cgit/linux/kernel/git/kdave/btrfs-progs.git/ Gitweb source viewer] of the userspace tools repository
+
  
=== Wiki editing ===
+
== News ==
  
The wiki contributions are welcome! Please create an account and wait for approval (this is a necessary spam protection). You can try to catch some of the wiki admins on [[#Project_information.2FContact|IRC]] and expedite the account creation.
+
''' btrfs-progs v5.18.1 (June 2022) '''
 +
* Please see the release notes at [https://btrfs.readthedocs.io/en/latest/CHANGES.html#btrfs-progs-5-18-1-2022-06-06 readthedocs.io]
  
 +
''' util-linux v2.38 (Apr 2022) '''
 +
 +
blk* utilities and libraries finally recognize btrfs formatted with zoned mode
 +
 +
''' linux v5.17 (Mar 2022) '''
 +
 +
Features:
 +
* make send work with concurrent block group relocation
 +
* new exclusive operation 'balance paused' to allow adding a device to filesystem with paused balance
 +
* new sysfs file for fsid stored in the per-device directory to help distinguish devices when seeding is enabled
 +
 +
Performance:
 +
* less metadata needed for directory logging, directory deletion is 20-40% faster
 +
* in zoned mode, cache zone information during mount to speed up repeated queries (about 50% speedup)
 +
* free space tree entries get indexed and searched by size (latency -30%, search run time -30%)
 +
* less contention in tree node locking when inserting a key and no splits are needed (files/sec in fsmark improves by 1-20%)
 +
 +
Fixes:
 +
* defrag rewrite from 5.16 fixed
 +
* get rid of warning when mounted with flushoncommit
 +
 +
Core:
 +
* global reserve stealing got simplified and cleaned up in evict
 +
* more preparatory work for extent tree v2
 +
* remove readahead framework
 +
* error handling improvements
 +
 +
</div>
 +
 +
<!-- Changelog Block -->
 +
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#dfefdf; align:left; margin-top:10px">
 +
 +
== Changelog ==
 +
 +
Read about past releases in the separate [[Changelog]] page
 +
 +
* [[Changelog#By_feature|features by kernel version]]
 +
* [[Changelog#By_version_.28linux_kernel.29|kernel changes for each release]]
 +
* <s>[[Changelog#By_version_.28btrfs-progs.29|btrfs-progs changes for each release (wiki)]]</s> btrfs-progs changes for each release https://btrfs.readthedocs.io/en/latest/CHANGES.html
 +
</div>
 +
 +
<!-- Source code Block -->
 +
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#dfefdf; align:left; margin-top:10px">
 +
 +
== Source code download ==
 +
 +
[[Btrfs source repositories]] describes purpose and contents, here are a few quick links:
 +
 +
* repository for kernel pull requests: git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git ([https://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git gitweb])
 +
* kernel development repository: git://github.com/kdave/btrfs-devel.git ([https://github.com/kdave/btrfs-devel.git web access])
 +
* kernel development repository (mirror): git://gitlab.com/kdave/btrfs-devel.git ([https://gitlab.com/kdave/btrfs-devel.git web access])
 +
* btrfs-progs development and release repository: git://github.com/kdave/btrfs-progs.git ([https://github.com/kdave/btrfs-progs.git web access])
 +
* released tarballs of btrfs-progs: https://mirrors.edge.kernel.org/pub/linux/kernel/people/kdave/btrfs-progs/
 +
</div>
 +
 +
<!-- Articles Block -->
 +
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#dfefdf; align:left; margin-top:10px">
 
== Articles, presentations, podcasts ==
 
== Articles, presentations, podcasts ==
 +
* '''Video:''' [https://www.youtube.com/watch?v=U7gXR2L05IU Deploying Btrfs at Facebook Scale] by Josef Bacik at the Open Source Summit 2020 (2020-06-29)
 
* '''Video:''' [https://youtu.be/qHalOdCZO9Q btrfs is awesome, except when it isn't] by Richard Brown at openSUSE Conferece 2018 (2018-05-25)
 
* '''Video:''' [https://youtu.be/qHalOdCZO9Q btrfs is awesome, except when it isn't] by Richard Brown at openSUSE Conferece 2018 (2018-05-25)
 
* '''Video:''' [https://youtu.be/-m01x3gHNjg btrfs: The Best Filesystem You've Never Heard Of] by poiupoiu at PhreakNIC 21 (2017-11-3)
 
* '''Video:''' [https://youtu.be/-m01x3gHNjg btrfs: The Best Filesystem You've Never Heard Of] by poiupoiu at PhreakNIC 21 (2017-11-3)
Line 207: Line 224:
 
* '''Technical report:''' [http://domino.watson.ibm.com/library/cyberdig.nsf/1e4115aea78b6e7c85256b360066f0d4/9e29fdded06e5de785257c1d005e7e9e!OpenDocument 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.
 
* '''Technical report:''' [http://domino.watson.ibm.com/library/cyberdig.nsf/1e4115aea78b6e7c85256b360066f0d4/9e29fdded06e5de785257c1d005e7e9e!OpenDocument 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:''' [http://dl.acm.org/citation.cfm?id=2501623 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 [https://sites.google.com/site/ohadrodehshomepage/research] page. Otherwise, try [http://domino.research.ibm.com/library/cyberdig.nsf/papers/6E1C5B6A1B6EDD9885257A38006B6130/$File/rj10501.pdf IBM Research link]
 
* '''Paper:''' [http://dl.acm.org/citation.cfm?id=2501623 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 [https://sites.google.com/site/ohadrodehshomepage/research] page. Otherwise, try [http://domino.research.ibm.com/library/cyberdig.nsf/papers/6E1C5B6A1B6EDD9885257A38006B6130/$File/rj10501.pdf IBM Research link]
 +
</div>
  
<!--
+
<!-- Historical Block -->
== Benchmarking ==
+
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#dfefdf; align:left; margin-top:10px">
-->
+
 
+
 
== Historical resources ==
 
== Historical resources ==
  
Line 218: Line 234:
 
=== Articles, presentations, podcasts ===
 
=== Articles, presentations, podcasts ===
  
 +
* [http://marc.merlins.org/perso/btrfs/post_2014-05-21_My-Btrfs-Talk-at-Linuxcon-JP-2014.html Marc MERLIN's Btrfs talk at Linuxcon JP 2014] which gives an overview of Btrfs, best practices, and its more interesting features.
 
* '''Article:''' [http://www.howtoforge.com/a-beginners-guide-to-btrfs A Beginner's Guide To Btrfs] (2012-11-26)
 
* '''Article:''' [http://www.howtoforge.com/a-beginners-guide-to-btrfs A Beginner's Guide To Btrfs] (2012-11-26)
 
* '''Article:''' [http://www.oracle.com/technetwork/articles/servers-storage-admin/advanced-btrfs-1734952.html How I Use the Advanced Capabilities of Btrfs] by Margaret Bierman with Lenz Grimmer (2012-08-11)
 
* '''Article:''' [http://www.oracle.com/technetwork/articles/servers-storage-admin/advanced-btrfs-1734952.html How I Use the Advanced Capabilities of Btrfs] by Margaret Bierman with Lenz Grimmer (2012-08-11)
Line 230: Line 247:
 
* '''Webcast:''' [https://event.on24.com/eventRegistration/EventLobbyServlet?target=registration.jsp&eventid=233161&sessionid=1&key=D0B1D3285FA444C5745C344A1C859CE0&partnerref=banner&sourcepage=register State of "Btrfs" File System for Linux by Chris Mason] (2010-08-26) [email registration and flash required]
 
* '''Webcast:''' [https://event.on24.com/eventRegistration/EventLobbyServlet?target=registration.jsp&eventid=233161&sessionid=1&key=D0B1D3285FA444C5745C344A1C859CE0&partnerref=banner&sourcepage=register State of "Btrfs" File System for Linux by Chris Mason] (2010-08-26) [email registration and flash required]
 
* '''Article:''' [http://lwn.net/Articles/342892/ Valerie Aurora: A short history of btrfs] (2009-07-22)
 
* '''Article:''' [http://lwn.net/Articles/342892/ Valerie Aurora: A short history of btrfs] (2009-07-22)
 +
</div>
 +
 +
<!-- Project Block -->
 +
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#dfefdf; align:left; margin-top:10px">
 +
 +
== Project information/Contact ==
 +
 +
* Development statistics, contributors, commits — https://btrfs.readthedocs.io/en/latest/Contributors.html#statistics-for-5-x-series
 +
* [https://btrfs.readthedocs.io/en/latest/Glossary.html Glossary]
 +
* Contact information:
 +
** [[Btrfs mailing list]]
 +
** [http://en.wikipedia.org/wiki/Internet_Relay_Chat IRC] on [https://libera.chat libera.chat] in the channel [irc://irc.libera.chat:6667/btrfs #btrfs]
 +
** Reporting bugs:
 +
*** for kernel code see [[Problem_FAQ#How_do_I_report_bugs_and_issues.3F | the Bugzilla FAQ]], quick tip: use product ''File System'' and component ''btrfs''.
 +
*** for btrfs-progs please use [https://github.com/kdave/btrfs-progs/issues/ github issues] (and not kernel.org bugzilla anymore)
 +
*** for documentation please use [https://github.com/kdave/btrfs-progs/issues/ github issues]
 +
* [[Project ideas]]
 +
* [[Project_ideas#Cleanup_projects|Cleanup ideas]]
 +
* [[Project_ideas#Userspace_tools_projects|Userspace tools projects]]
 +
</div>
 +
 +
<!-- Wiki Block -->
 +
<div style="margin:0; margin-top:10px; border:1px solid #dfdfdf; padding: 0em 1em 1em 1em; background-color:#dfefdf; align:left; margin-top:10px">
 +
 +
== Wiki accounts, editing ==
 +
 +
The wiki is still in use, however the main portion of documenation is being migrated to https://btrfs.readthedocs.io.
 +
 +
Wiki edits and fixups are welcome and may be copied to the RTD documentation eventually. 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 [[#Project_information.2FContact|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.
 +
</div>
  
=== Benchmarks ===
+
|}
* '''2019-12''' [https://www.phoronix.com/scan.php?page=article&item=linux54-hdd-raid&num=1 Linux 5.4 EXT4 / XFS / Btrfs RAID Performance On Four HDDs]
+
* '''2012-10''' [http://www.ilsistemista.net/index.php/linux-a-unix/36-btrfs-mount-options-and-virtual-machines-an-in-depth-look.html BTRFS, mount options and virtual machines: an in-depth look] (Ilsistemista.net)
+
* '''2010-10''' [http://www.linux-mag.com/id/7876 One Billion Files] Btrfs performs well in comparison to other filesystems, when there are a billion files in the filesystem.
+

Revision as of 14:05, 15 June 2022

btrfs

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 by multiple companies (https://btrfs.readthedocs.io/en/latest/Contributors.htm, 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.

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
    • 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)
  • 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
  • Seeding 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 and backup
  • 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)
  • fsverity integration

Features by kernel version

Features Currently in Development or Planned for Future Implementation

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

Documentation

Documentation

Guides and usage information

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

News

btrfs-progs v5.18.1 (June 2022)

util-linux v2.38 (Apr 2022)

blk* utilities and libraries finally recognize btrfs formatted with zoned mode

linux v5.17 (Mar 2022)

Features:

  • make send work with concurrent block group relocation
  • new exclusive operation 'balance paused' to allow adding a device to filesystem with paused balance
  • new sysfs file for fsid stored in the per-device directory to help distinguish devices when seeding is enabled

Performance:

  • less metadata needed for directory logging, directory deletion is 20-40% faster
  • in zoned mode, cache zone information during mount to speed up repeated queries (about 50% speedup)
  • free space tree entries get indexed and searched by size (latency -30%, search run time -30%)
  • less contention in tree node locking when inserting a key and no splits are needed (files/sec in fsmark improves by 1-20%)

Fixes:

  • defrag rewrite from 5.16 fixed
  • get rid of warning when mounted with flushoncommit

Core:

  • global reserve stealing got simplified and cleaned up in evict
  • more preparatory work for extent tree v2
  • remove readahead framework
  • error handling improvements

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 is still in use, however the main portion of documenation is being migrated to https://btrfs.readthedocs.io.

Wiki edits and fixups are welcome and may be copied to the RTD documentation eventually. 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.

Personal tools