Revision 47 as of 2010-07-03 16:16:55

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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 b trees 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 install cd from http://cdimage.ubuntu.com/

Do a regular installation except use manual partitioning to create:

  • a ext2 or ext3 partition of about 250MB 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

Snapshots & Subvolumes

Create a subvolume: 

btrfs subvolume create test

This creates a subvolume in your home area called test. It appears to be a directory.

Do a snapshot copy of a subvolume: 

btrfs subvolume snapshot test snap-copy-one

This creates a subvolume in your home area called snap-copy-one complete with all the data contained in test at the time of the snapshot.

List your subvolume: 

sudo btrfs subvolume list test

This lists your subvolumes. Root privileges and the name of one of your subvolumes is required.

Sample Output: 

ID 264 top level 5 path home/myhome/test
ID 265 top level 5 path home/myhome/snap-copy-one

Delete your subvolume: 

sudo btrfs subvolume delete test

Root privileges are required to delete subvolumes.

Adding Filesystem Compression

Edit /etc/fstab: 

# <file system>                      <mount point>    <type>  <options>          <dump>  <pass>
proc                                          /proc   proc    nodev,noexec,nosuid   0       0
# / was on /dev/sda2 during installation
UUID=07e198ed-18a3-41ed-9e48-bde82ead65fc     /       btrfs   defaults, compress    0       1
# /boot was on /dev/sda1 during installation
UUID=90983817-83f8-464f-a50c-39cd02317447     /boot   ext2    defaults              0       2
# swap was on /dev/sda5 during installation
UUID=a3da3212-876f-4350-94b3-4b5b5040c871     none    swap    sw                    0       0

The compress option was added. Remount the filesystem via a reboot.

Display 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

Show Filesystem Information for a path: 

btrfs filesystem df /home/myhome

Displays information about path /home/myhome.

Sample Output: 

Metadata: total=640.00MB, used=265.57MB
Data: total=27.00GB, used=26.54GB
System: total=12.00MB, used=12.00KB

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

Links