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** [[Gotchas]] — lists known bugs and issues, but not necessarily solutions.
 
** [[Gotchas]] — lists known bugs and issues, but not necessarily solutions.
  
=== Project information ===
+
=== Project information/Contact ===
  
 
* [[Changelog]] — history of changes in linux kernel wrt btrfs
 
* [[Changelog]] — history of changes in linux kernel wrt btrfs

Revision as of 23:08, 25 June 2013

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 Oracle, Red Hat, Fujitsu, Intel, SUSE, STRATO and many others, Btrfs is licensed under the GPL and open for contribution from anyone.

Btrfs is under heavy development, but every effort is being made to keep the filesystem stable and fast. Because of the speed of development, you should run the latest kernel you can (either the latest release kernel from kernel.org, or the latest -rc kernel. Please email the Btrfs mailing list if you have any problems or questions while using Btrfs.

Contents

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.

The main Btrfs features available at the moment include:

  • Extent based file storage
  • 2^64 byte == 16 EiB maximum file size
  • 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
  • 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

Additional features in development, or planned, include:

  • Very fast offline filesystem check
  • Object-level mirroring and striping
  • Alternative checksum algorithms
  • Online filesystem check
  • Other compression methods (snappy, lz4)
  • Hot data tracking and moving to faster devices (currently being pushed as a generic feature available through VFS)
  • Deduplication (online, offline)

News

Coming in 3.10 (highlights or user visible changes)

  • reduced size of metadata by so-called skinny extents [1]
  • enhanced syslog message format [2]
  • the mount option subvolrootid is deprecated
  • lots of stability improvements, removed many BUG_ONs
  • qgroups are automatically created when quotas are enabled [3]
  • qgroups are able to rescan current filesystem and sync the quota state with the existing subvolumes
  • enhanced send/recv format for multiplexing more data into one stream [4]
  • various unsorted code cleanups, minor performance updates

Enterprise btrfs support (Feb 2012)

  • Since February 2012 there are two vendors who support btrfs in their distributions, Oracle and SUSE.

Read about past releases in the Changelog

Articles, presentations, podcasts

Documentation

Guides and usage information

Project information/Contact

Using the built-in tools

  • btrfs — main administration tool
  • mkfs.btrfs — creating the filesystem
  • btrfsck — repairing file systems
  • restore and find-root — utilities to find and restore data from an unmountable filesystem
  • btrfs-convert — tool to convert in-place from ext2/3/4 filesystems to btrfs

Developer documentation

  • 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

Source code download

Benchmarking

Personal tools