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 by Oracle, Red Hat, Fujitsu, Intel, SUSE and many others, Btrfs is licensed under the GPL and open for contribution from anyone.
- 1 Recent Developments and News Links
- 2 Installation
- 3 Creating a Btrfs Partition
- 4 Btrfs Features
- 5 Resources
Recent Developments and News Links
- Avi Miller presenting BTRFS at SCALE 10x. Jan/2012.
- Summary of Chris Mason's talk from LFCS 2012
- On 2012-03-28, 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 of 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 thepackage (as a module). User space utilities are available in .
For multi-devices support (RAID like feature of btrfs) aka btrfs volume in early boot, you have to enable btrfs mkinitcpio hook (provided by mkinitcpio package) to be able to use, for example, a root btrfs volume. If the btrfs volume is a non-system volume, one only needs to set USEBTRFS="yes" in /etc/rc.conf
However, if you only use bare btrfs partition, such options are not needed.
For more options/features, users may want to install AUR. This package will install a mkinitcpio hook called btrfs_advanced intended for those who wish to have automatic rollback feature.AUR from the
Creating a Btrfs Partition
Format a New Partition to Btrfs
# mkfs.btrfs [options] dev [dev ...]
One can select multiple devices to create a RAID. Supported RAID levels include RAID 0, RAID 1 and RAID 10. By default, metadata is mirrored and data is striped.
Convert Ext3/4 to Btrfs
- Boot a live CD (Arch for example)
- Enable [remote-core] and [remote-testing]
- Setup the network
- Install btrfs-progs (make sure versions of dependencies match: glibc, e2fsprogs)
- Mount the converted partition and modify the
/etc/fstabfile specifying either
btrfsfor the partition type.
- Chroot into the system and rebuild the GRUB entry (see Install from Existing Linux and GRUB articles, if unfamiliar with this procedure).
After btrfs-convert, and confirming everything works, if you want to make the change permanent, you need to delete the saved image, delete the subvolume that image is on, then balance the drive to reclaim the space. For example, after converting /home to btrfs:
rm /home/ext2_saved/* btrfs subvolume delete /home/ext2_saved btrfs filesystem balance /home
Note: the last command will take a while on a large partition with much data.
CoW comes with some advantages, but can negatively affect performance with large files that have small random writes. It is recomended to disable CoW for database files and virtual machine images. You can disable CoW for the entire block device by mounting it with "nodatacow" option. However, this will disable CoW for the entire file system. To disable CoW for single files/directories, use the following command:
# chattr +C [file/directory path]
Note, from chattr man page: For btrfs, the 'C' flag should be set on new or empty files. If it is set on a file which already has data blocks, it is undefined when the blocks assigned to the file will be fully stable. If the 'C' flag is set on a directory, it will have no effect on the directory, but new files created in that directory will have the No_COW attribute.
Multi-device filesystem and RAID feature
When creating a btrfs filesystem, you can pass as many partitions or disk devices as you want to mkfs.btrfs. The filesystem will be created across these devices. You can "merge" this way, multiple partitions or devices to get a big btrfs filesystem.
You can also add or remove device from an existing btrfs filesystem (caution is mandatory).
A multi-device btrfs filesystem (also called a btrfs volume) is not recognized until
# btrfs device scan
has been run. This is the purpose of the btrfs mkinitcpio hook or the USEBTRFS variable in /etc/rc.conf
When creating multi-device filesystem, you can also specify to use RAID0, RAID1 or RAID10 across the devices you have added to the filesystem.
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.
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=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 storage drive, simply switch to another terminal (Template:Keypress), and run the following command:
# mount -o remount,compress=lzo /dev/sdXY /mnt/target
After the installation is finished, add
compress=lzo to the mount options of the root filesystem in