Difference between revisions of "Btrfs"

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[[Category:File systems (English)]]
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Revision as of 14:45, 23 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 Oracle Linux 6 and backported to 5.
  • Arch Linux supplies this version in core/btrfs-progs (since version 0.19.20120328-1).


Btrfs support is included in the the core/linux package (hardcoded into the kernel). User space utils are available from [core]:

# pacman -S btrfs-progs

If using btrfs as the root filesystem, users may 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

# 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. modprobe btrfs
  5. Install btrfs-progs (make sure versions of dependencies match: glibc,e2fsprogs)
  6. Run btrfs-convert
  7. Mount the converted partition and modify the /etc/fstab specifying either 'auto' or 'btrfs' for the partition type.
  8. 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.