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BTRFS as root filesystem

System overview

  1. /dev/sda1 4.08GB ext4 “/” used 1.56GB, free 2.53GB
  2. /dev/sda2 10.91GB extended
    1. /dev/sda5 524MB swap
    2. /dev/sda6 10.40GB ext4 “/home” 321MB used, 10.09GB free

Boot from live-cd

Btrfs support is heavily developed in Linux Kernel. So do not use old kernel.

I was using gparted-live-0.22.0-1-amd64.iso (NOTE: to match your existing system architecture (i586, amd64, etc)) Which contains:

  1. Kernel 3.16.0-4-586
  2. btrfs utils version 3.17

Conversion

fsck -f /dev/sda1
fsck -f /dev/sda6
 
btrfs-convert /dev/sda1
Disk usage before conversion: used 1.56GB, free 2.53GB
after conversion: used 1.65GB, free 2.43GB
btrfs check /dev/sda1

Update system

Mount new root filesystem: 

mount /dev/sda1 /mnt
for i in dev dev/pts proc sys ; do mount --bind /$i /mnt/$i ; done
chroot /mnt

get new UUID of /dev/sda1 using “blkid” mount /dev/sda1 somewhere, go to etc/fstab and update to new UUID: 

UUID=a74f5787-aee1-4981-b7e6-fbd3cb6ac919 /               btrfs    defaults 0       1
update-grub
grub-install /dev/sda
 
exit
 
reboot

and remove Live CD with Gparted

rollback to ext FS

Rollback to ext2 is possible. There is subvolume ext2_saved on filesystem. 

btrfs subvolume list /

To delete backup 

btrfs subvolume delete /ext2_saved

Update to kernel 4

Edit /etc/apt/sources and add sid release 

apt-get update
apt-get install linux-image-amd64
apt-get install btrfs-tools
update-initramfs -u
  • ERROR: Warning: /sbin/fsck.btrfs doesn't exist, can't install to initramfs, ignoring.
  • EXPLANATION: “This is going to be changed back in the next version of btrfs-tools.”
  • SOLUTION: ln -s /bin/fsck.btrfs /sbin/fsck.btrfs

Check btrfs-tools version 

/bin/btrfs version

Converting dirs into subvolumes

To make backups, snapshoting, moving much easier and faster, every directory you want to backup by snapshot should be a subvolume. Also root filesystem should be created in separate subvolume not in btrfs root.

To distinguish volumes from directories we will use @ character at beginning of subvolume name. This is Ubuntu naming convention for subvolumes.

Proposed subvolumes structure /@ /@home /@var

root

  • take a snapshot of root volume
    • btrfs subvolume snapshot . @root
  • make @root subvolume a default root
    • update
      /etc/fstab
            UUID=739e6086-d925-4bdb-94f5-26d8c10dc171	/	btrfs	defaults,subvol=@root

or

  • set @root subvolume default mount path btrfs subvolume set-default @root /
  • move directory to subvolume (cp –reflink is much faster on BTRFS)

subdirectories

  • On BTRFS root create a new subvolume
    • btrfs subvolume create /mnt/btrfs/@home
  • move files into the new subvolume as if it were a directory
    • mv /mnt/btrs/@/home/* /mnt/btrfs/@home/
  • remove old directory
    • rmdir /mnt/btrfs/@/home
  • update /etc/fstab to mount @home as /home