Difference between revisions of "Btrfs"

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== Recent Developments ==
== Recent Developments ==
*With the release of the Linux kernel v3.3, Btrfs has been declared stable.
*On 28-Mar-2012, btrfs-progs includes btrfsck, a tool that can fix errors on btrfs filesystems.
*On 28-Mar-2012, btrfs-progs includes btrfsck, a tool that can fix errors on btrfs filesystems.
*Oracle has packaged this version of btrfs-progs and released it to their customers in Oracle Linux 5 and 6.
*Oracle has packaged this version of btrfs-progs and released it to their customers in Oracle Linux 5 and 6.

Revision as of 02:19, 9 April 2012

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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 and many others, Btrfs s licensed under the GPL and open for contribution from anyone.

Recent Developments

  • On 28-Mar-2012, btrfs-progs includes btrfsck, a tool that can fix errors on btrfs filesystems.
  • Oracle has packaged this version of btrfs-progs and released it to their customers in Oracle Linux 5 and 6.
  • Tom Gundersen pushed btrfs-progs-0.19.20120328-1 into [testing] thus adding Arch, to the growing list of distros that have btrfsfsck.


To install:

# pacman -S btrfs-progs

If using btrfs as the root filesystem, users may also want to install mkinitcpio-btrfs from AUR. This package will install a mkinitcpio hook intended for those who wish to have a single or multi-drive BTRFS file system as their / (root). The hook will ensure that the chosen root device from the kernel command line is intact and safe to boot. If root is not a BTRFS device, the hook is quietly skipped.

Basic Use

Format a New Partition to Btrfs

To format a device to btrfs

# mkfs.btrfs [options] dev [dev ...]

One can select multiple devices to create a raid. Supported raids include raid1, raid0, and raid 10. By default, metadata is mirrored and data is striped.

Convert Ext3/4 to Btrfs

Warning: Grub cannot boot btrfs root. Users need to install either Grub2 or Syslinux! This guide assumes users are aware of this limitation to Grub.
  1. Boot a live CD (Arch for example)
  2. Enable [remote-core] and [remote-testing]
  3. Setup the network
  4. Install btrfs-progs
  5. modprobe btrfs
  6. Run btrfs-convert

Once completed:

  1. Mount the converted partition and modify the /etc/fstab specifying either 'auto' or 'btrfs' for the partition type.
  2. Chroot into the system and rebuild the grub2 entry (see Install from Existing Linux and Grub2 articles if unfamiliar with this procedure.


One of the features of btrfs is the use of subvolumes. Subvolumes are basically a named btree that holds files and directories. They have inodes inside the tree of tree roots and can have non-root owners and groups. Subvolumes can optionally be given a quota of blocks. All of the blocks and file extents inside of subvolumes are reference counted to allow snapshotting. Similar to the dynamically expanding storage of a virtual machine that will only use as much space on a device as needed. Eliminating several half-filled partitions. One can also mount the subvolumes with different mount options giving more flexibility in security.

To create a subvolume:

# btrfs subvolume create [<dest>/]

For increased flexibility, install your system INTO A DEDICATED SUBVOLUME, and use:

rootflags=subvol=<whatever you called the subvol>

In the kernel boot parameters. It makes system rollbacks possible.

If using for the root partition, it is advisable to add crc32c to the modules array in /etc/mkinitcpio.conf as well as adding btrfs to the HOOKS array in /etc/mkinitcpio.conf.


To create a snapshot:

# btrfs subvolume snapshot <source> [<dest>/]<name>

Snapshots are not recursive, this means that every subvolume inside subvolume will be an empty directory inside the snapshot.


Btrfs supports online defragmentation. To defragment the metadata of the root folder, simply do:

# btrfs filesystem defragment /

This will not defragment the entire system. For more information, see this page on the btrfs wiki.


Btrfs supports transparent compression, which means every file on the partition is automatically compressed. This does not only reduce the size of those files, but also improves performance, in particular if using the lzo algorithm. Compression is enabled using the compress=gzip or compress=lzo mount options. Only files created or modified after the mount option is added will be compressed, so to fully benefit from compression it should be enabled during installation. After preparing the hard drive, simply switch to another terminal (Ctrl+Alt+number), and run the following command:

# mount -o remount,compress=lzo /dev/partition /mnt/target # note: replace /dev/partition by the partition on which Arch Linux is installed.

Verify if compression is enabled with the mount command. After the installation is finished, add compress=lzo to the mount options of the root filesystem in /etc/fstab.


Tango-view-refresh-red.pngThis article or section is out of date.Tango-view-refresh-red.png

Reason: This section is out-of-date now that the stable release of btrfs-progs has hit [testing]. This version contains a btrfsfsck that can repair the filesystem. (Discuss in Talk:Btrfs#)

Problems with operations on files, silent fails of copying

Fiemap support was implemented badly in kernels older than mainline 2.6.38-rc6-git6 kernel - which was proved by coreutils package in version 8.10 and its internal copying function (first with fiemap support).

The bug exist only if compressed btrfs volume is present and can cause lots of damage like the installation of broken packages.

coreutils 8.10 + kernel<2.6.38-rc6-git6 + compresses btrfs = really bad idea.

If using older kernels, either turn btrfs' compression off or downgrade coreutils.

TroubleShooting Links

Segfault after power failure upon mounting root

After power failures Btrfs ends up not booting, instead just segfaulting. This can be fixed with

btrfs-zero-log /dev/sdX#

. To build btrfs-zero-log, you need to get it from the git:

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git
$ make 
$ make btrfs-zero-log

If the build fails with

ctree.c: In function '__btrfs_cow_block':
ctree.c:265:6: error: variable 'generation' set but not used [-Werror=unused-but-set-variable]

, you need to patch the makefile with -Wno-error to make it ignore errors.

btrfs-zero-log is also now available in AUR pkg btrfs-progs-gitAUR.

Original thread

If one still has issues, check the official BTRFS Problem FAQ in their Wiki at https://btrfs.wiki.kernel.org/index.php/Problem_FAQ

Also have a look to use up to date source code repositories for btrfs-progs and kernel, try the integration repositories as well: https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories


  • Btrfs Wiki - The kernel.org wikis are read-only since the hack; this is read/write mirror.
  • Funtoo Btrfs wiki entry - Very well-written albeit slightly out dated article.