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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 to choose from, 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
  • Compression (zlib and LZO)
  • Integrated multiple device support
    • File Striping, File Mirroring, and File Striping+Mirroring 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.

Additional features in development, or planned, include:

  • Very fast offline filesystem check
  • File Striping with Single and Dual Parity
  • Object-level mirroring and striping
  • Alternative checksum algorithms
  • Online filesystem check
  • Efficient incremental filesystem mirroring
  • Other compression methods (snappy, lz4)
  • Hot data tracking and moving to faster devices
  • Subvolume-aware quota support
  • Send/receive of changes

News

Coming in Linux 3.6

  • subvolume-aware quotas (qgroups)
  • support for send/receive between snapshot changes (LWN article)
  • atime is not updated on read-only snapshots (LWN article)
  • cross-subvolume file clone (aka. reflink)
  • remount with no compression possible
  • new ioctl to read device readiness status
  • speed improvement for concurrent multithreaded reads

2012-05-07

Latest btrfs-progs (c. 26 Mar 2012)

  • btrfsck can now repair some forms of filesystem breakage

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

Contact

Source Code Download

Benchmarking

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

Planning

Personal tools