Revision 31 as of 2010-06-27 13:35:09

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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 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

How to install

Ubuntu 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

Ubuntu 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

How to Validate Filesystem Integrity

Fsck a device: 

sudo btrfsck /dev/sda2

Does online filesystem check of device /dev/sda2.

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.

How to 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

Troubleshooting

Alternatives

  • Tux3?
  • ZFS over Fuse?

  • Hammer FS (DragonFly BSD)

Links