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What is btrfs?
The B tree file system is a “copy-on-write (COW)” check-summed file system with multi-device support and writable snapshots.
A snapshot is a frozen image of the file system at a point in time. This feature facilitates system rollback and instant backup when combined with supporting software.
Btrfs uses Rodeh's btrees which are COW friendly.
Check-summing is a data integrity method.
Multi-device support is part of the subvolume structure btrfs uses to grow or shrink a file system.
“A short history of btrfs” (LWN.NET July 22, 2009) by Valerie Aurora (formerly Henson) is available at http://lwn.net/Articles/342892/
More Information on btrfs is available at https://btrfs.wiki.kernel.org/index.php/Main_Page and http://en.wikipedia.org/wiki/Btrfs
Features
- Extent based file storage (2^64 max file size)
- Space efficient packing of small files
- Space efficient indexed directories
- Dynamic inode allocation
- Writable snapshots
- Subvolumes (separate internal filesystem roots)
- Object level mirroring and striping
- Checksums on data and metadata (multiple algorithms available)
- Compression
- Integrated multiple device support, with several raid algorithms
- Online filesystem check
- Very fast offline filesystem check
- Efficient incremental backup and FS mirroring
- Online filesystem defragmentation
Installing on 10.10 Maverick
Obtain the latest alternative install cd from http://cdimage.ubuntu.com/
Do a regular installation except use manual partitioning to create:
- a ext2 or ext3 partition of about 512 to 1024 MB for /boot
- a btrfs partition for /
- a linux swap partition about 2.5 times your memory
Installing on 8.10 Intrepid
PPA deb packages
https://launchpad.net/~brcha/+archive/ppa
Lines for sources.list.d:
deb http://ppa.launchpad.net/brcha/ppa/ubuntu intrepid main deb-src http://ppa.launchpad.net/brcha/ppa/ubuntu intrepid main
Add the GPG key:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 17f547c39c5c4071e254d0a7313d312748a22a95
Download module source and btrfs tools:
sudo apt-get install btrfs btrfs-progs module-assistant
Build and install kernel module:
sudo module-assistant auto-install btrfs sudo modprobe btrfs
Compile from Source
NOT ACTUALLY WORKING YET
btrfs wiki getting started page
Kernel Module Dependencies
8.10 Kernel 2.6.27-9-generic
- CONFIG_LIBCRC32C=m
- CONFIG_ZLIB_INFLATE=y
- CONFIG_ZLIB_DEFLATE=m
- build-essential: make, compiler, etc
- linux-headers-2.6.27-9-generic: latest kernel headers
sudo apt-get install build-essential linux-headers-2.6.27-9-generic
Patch: http://permalink.gmane.org/gmane.comp.file-systems.btrfs/2562
Download, patch and compile code:
wget http://www.kernel.org/pub/linux/kernel/people/mason/btrfs/btrfs-0.17.tar.bz2 tar -jxvf btrfs-0.17.tar.bz2 cd btrfs-0.17 #apply patch make
Currently btrfs does not work with kernel 2.6.27
Ensure modules are up and running, and insert btrfs module into kernel.
sudo modprobe libcrc32c zlib_inflate zlib_deflate sudo insmod btrfs.ko
btrfs progs dependencies
sudo apt-get install e2fsprogs uuid-dev
wget http://www.kernel.org/pub/linux/kernel/people/mason/btrfs/btrfs-progs-0.17.tar.bz2 tar -jxvf btrfs-progs-0.17.tar.bz2 make
btrfs-progs compile fine
Show Filesystem Information
Show a device:
sudo btrfs filesystem show /dev/sda2
Displays information about device /dev/sda2.
Sample Output:
failed to read /dev/sr0
Label: none uuid: 07e198ed-18a3-41ed-9e48-bde82ead65fc
Total devices 1 FS bytes used 26.80GB
devid 1 size 912.20GB used 28.27GB path /dev/sda2
Btrfs Btrfs v0.19
Validate Filesystem Integrity
Fsck a device:
sudo btrfsck /dev/sda2
Does online filesystem check of device /dev/sda2.
Sample Output:
found 28752076800 bytes used err is 0 total csum bytes: 27806792 total tree bytes: 277921792 total fs tree bytes: 233484288 btree space waste bytes: 76057148 file data blocks allocated: 35377807360 referenced 28362235904 Btrfs Btrfs v0.19
Scrub a directory:
Install btrfs-scrub using instructions at http://xercestech.com/how-to-scrub-btrfs.geek
btrfs-scrub Videos
The btrfs-scrub routine reads every file in the directory Videos. Use dmesg to view errors.
Improve Filesystem Performance
Balance the B-Tree:
btrfs filesystem balance /home/myhome
In this case the Rodeh b-trees in path /home/myhome are being balanced. This could take some time.
Defragment a directory:
sudo btrfs filesystem defragment Videos
All the files in the Videos directory are defragmented. Sudo is required to get ioctl access to the files.
How to use
- How to format disk as btrfs
- How to grow/shrink file system
- How to create snapshots
- How to access snapshots
- How to convert ext2/3(/4?) partitions to btrfs
- How to create an image of a btrfs file system
- How to restore from an image of a btrfs file system
- How to recover from a failed device
- How to add another device to file system
btrfs wiki documentation category