How To Convert An ext3/ext4 Root File System To btrfs On Ubuntu 12.10

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Submitted by falko (Contact Author) (Forums) on Sun, 2012-11-25 19:29. :: Ubuntu | Storage

How To Convert An ext3/ext4 Root File System To btrfs On Ubuntu 12.10

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Author: Falko Timme <ft [at] falkotimme [dot] com>
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Last edited 11/23/2012

ext3 and ext4 file systems can be converted to btrfs. For non-root file systems, this can be done online (i.e., without reboot), while for root file systems we need to boot into some kind of rescue system or Live CD. This guide explains how to convert an ext3 or ext4 root file system into btrfs on Ubuntu 12.10 and how to roll back to ext3/ext4 again if desired.

I do not issue any guarantee that this will work for you!

 

1 Preliminary Note

I'm using a system here with one large / partition (i.e., no /boot partition) and without LVM. During initial installation, it was installed with the option Guided - Use entire disk. For different partition schemes, the procedure might differ.

My hard drive is named /dev/sda in this tutorial, my system partition is /dev/sda1.

I will use an Ubuntu 12.10 Desktop Live-CD as the rescue system throughout this tutorial.

I will show two ways of doing the conversion: one where we simply convert the system partition and change /etc/fstab, and one where we create the subvolumes @ and @home according to Ubuntu's btrfs partition layout (see https://help.ubuntu.com/community/btrfs) - this is slightly more complicated, but a must if you want to use apt-btrfs-snapshot which requires this subvolume layout.

A note for Ubuntu users:

Because we must run all the steps from this tutorial with root privileges, we can either prepend all commands in this tutorial with the string sudo, or we become root right now by typing

sudo su

 

2 Install btrfs-tools

On the original system, before we boot into the rescue system, install btrfs-tools so that the package is available when we chroot to the system partition in the rescue system (it is possible that we don't have a network connection for installing the package when we are chrooted into the system partition in the rescue system, that's why we should install it now):

apt-get install btrfs-tools

Now we must boot into some kind of rescue system with btrfs support. For example, you can insert the Ubuntu 12.10 Desktop CD into the CD drive (make sure it has the same architecture - i386 or x86_64 - as this system) and reboot:

reboot

 

3 Doing A Simple Conversion (No @ And @home Subvolumes)

In the rescue system, log in as root. Make sure that btrfs-tools are installed:

apt-get install btrfs-tools

Do a file system check...

fsck -f /dev/sda1

... and then run the conversion tool:

btrfs-convert /dev/sda1

root@ubuntu:~# btrfs-convert /dev/sda1
creating btrfs metadata.
creating ext2fs image file.
cleaning up system chunk.
conversion complete.
root@ubuntu:~#

Next we mount our system partition and chroot to it:

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

ls -l

As you see, there's now a folder called ext2_saved which contains an image of our system partition before the conversion (with the original ext3 or ext4 file system). This image can be used to do a rollback later on.

root@ubuntu:/# ls -l
total 20
drwxr-xr-x   1 root root 1938 Nov 22 13:15 bin
drwxr-xr-x   1 root root  326 Nov 23 18:38 boot
drwxr-xr-x  14 root root 4060 Nov 23 18:38 dev
drwxr-xr-x   1 root root 2820 Nov 23 18:38 etc
dr-xr-xr-x   1 root root   10 Nov 23 18:40 ext2_saved
drwxr-xr-x   1 root root   26 Nov 22 13:16 home
lrwxrwxrwx   1 root root   32 Nov 22 13:11 initrd.img -> boot/initrd.img-3.5.0-17-generic
lrwxrwxrwx   1 root root   33 Nov 22 13:11 initrd.img.old -> /boot/initrd.img-3.5.0-17-generic
drwxr-xr-x   1 root root  982 Nov 22 13:15 lib
drwxr-xr-x   1 root root   40 Nov 22 13:10 lib64
drwx------   1 root root    0 Nov 22 13:10 lost+found
drwxr-xr-x   1 root root   10 Nov 22 13:10 media
drwxr-xr-x   1 root root    0 Oct  9 17:03 mnt
drwxr-xr-x   1 root root    0 Oct 17 18:22 opt
dr-xr-xr-x 186 root root    0 Nov 23 18:38 proc
drwx------   1 root root   68 Nov 23 18:38 root
drwxr-xr-x   1 root root    0 Nov 22 13:16 run
drwxr-xr-x   1 root root 3094 Nov 23 18:38 sbin
drwxr-xr-x   1 root root    0 Jun 11 20:36 selinux
drwxr-xr-x   1 root root    0 Oct 17 18:22 srv
dr-xr-xr-x  13 root root    0 Nov 23 18:38 sys
drwxrwxrwt   1 root root    0 Nov 23 18:38 tmp
drwxr-xr-x   1 root root   70 Nov 22 13:10 usr
drwxr-xr-x   1 root root  114 Nov 23 18:38 var
lrwxrwxrwx   1 root root   29 Nov 22 13:11 vmlinuz -> boot/vmlinuz-3.5.0-17-generic
lrwxrwxrwx   1 root root   29 Nov 22 13:11 vmlinuz.old -> boot/vmlinuz-3.5.0-17-generic
root@ubuntu:/#

Run

blkid /dev/sda1

root@ubuntu:/# blkid /dev/sda1
/dev/sda1: UUID="63accb30-95b9-4268-ae1e-6d0ad3ef3a9d" UUID_SUB="d9521f58-91e5-44a7-a52e-9cfb0b3056ca" TYPE="btrfs"
root@ubuntu:/#

We need the UUID from the output for modifying /etc/fstab:

vi /etc/fstab

Comment out the old / partition line and add a new one. Replace the UUID with the UUID from the blkid output, then replace ext4 (or ext3) with btrfs, and finally replace the mount options (e.g. errors=remount-ro) with the string defaults:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sda1 during installation
#UUID=ad50ef37-797d-44ea-a8fa-ae61abe4d00f /               ext4    errors=remount-ro 0       1
UUID=63accb30-95b9-4268-ae1e-6d0ad3ef3a9d /               btrfs   defaults 0       1
# swap was on /dev/sda5 during installation
UUID=4dc578f3-c65c-4013-b643-72e70455b21b none            swap    sw              0       0

Next open /etc/grub.d/00_header...

vi /etc/grub.d/00_header

... and comment out line 93 (if [ -n "\${have_grubenv}" ]; then if [ -z "\${boot_once}" ]; then save_env recordfail; fi; fi):

[...]
function recordfail {
  set recordfail=1
  #if [ -n "\${have_grubenv}" ]; then if [ -z "\${boot_once}" ]; then save_env recordfail; fi; fi
}
[...]

If you don't do this, you will get the error...

error: sparse file not allowed

... when you boot from the btrfs file system, and you have to press ENTER to proceed with the boot process (see Ubuntu 12.10 + btrfs: error: sparse file not allowed).

Next run

update-grub
grub-install /dev/sda

and exit from the chroot:

exit

Reboot into the normal system (make sure you remove the Live CD from the CD drive):

reboot

If everything goes well, the system should come up without problems, now running on btrfs.

ls -l /

As you see, there's still the ext2_saved folder with the image of the original system in case you want to do a rollback:

root@server1:~# ls -l /
total 20
drwxr-xr-x   1 root root 1938 Nov 22 13:15 bin
drwxr-xr-x   1 root root  326 Nov 23 18:38 boot
drwxr-xr-x  14 root root 4080 Nov 23 18:43 dev
drwxr-xr-x   1 root root 2820 Nov 23 18:43 etc
dr-xr-xr-x   1 root root   10 Nov 23 18:40 ext2_saved
drwxr-xr-x   1 root root   26 Nov 22 13:16 home
lrwxrwxrwx   1 root root   32 Nov 22 13:11 initrd.img -> boot/initrd.img-3.5.0-17-generic
lrwxrwxrwx   1 root root   33 Nov 22 13:11 initrd.img.old -> /boot/initrd.img-3.5.0-17-generic
drwxr-xr-x   1 root root  982 Nov 22 13:15 lib
drwxr-xr-x   1 root root   40 Nov 22 13:10 lib64
drwx------   1 root root    0 Nov 22 13:10 lost+found
drwxr-xr-x   1 root root   10 Nov 22 13:10 media
drwxr-xr-x   1 root root    0 Oct  9 17:03 mnt
drwxr-xr-x   1 root root    0 Oct 17 18:22 opt
dr-xr-xr-x 100 root root    0 Nov 23 18:43 proc
drwx------   1 root root   84 Nov 23 18:42 root
drwxr-xr-x  17 root root  620 Nov 23 18:43 run
drwxr-xr-x   1 root root 3094 Nov 23 18:38 sbin
drwxr-xr-x   1 root root    0 Jun 11 20:36 selinux
drwxr-xr-x   1 root root    0 Oct 17 18:22 srv
dr-xr-xr-x  13 root root    0 Nov 23 18:43 sys
drwxrwxrwt   1 root root    0 Nov 23 18:42 tmp
drwxr-xr-x   1 root root   70 Nov 22 13:10 usr
drwxr-xr-x   1 root root  114 Nov 23 18:38 var
lrwxrwxrwx   1 root root   29 Nov 22 13:11 vmlinuz -> boot/vmlinuz-3.5.0-17-generic
lrwxrwxrwx   1 root root   29 Nov 22 13:11 vmlinuz.old -> boot/vmlinuz-3.5.0-17-generic
root@server1:~#

ls -l /ext2_saved/

root@server1:~# ls -l /ext2_saved/
total 1594360
-r-------- 1 root root 31137464320 Jan  1  1970 image
root@server1:~#

In fact, this is not a folder, it's a btrfs subvolume:

btrfs subvolume list /

root@server1:~# btrfs subvolume list /
ID 256 top level 5 path ext2_saved
root@server1:~#

If you are sure you want to stay with btrfs and don't want to do a rollback, you can delete that subvolume to free up some space:

btrfs subvolume delete /ext2_saved

Afterwards, the image should be gone:

ls -l /

root@server1:~# ls -l /
total 16
drwxr-xr-x  1 root root 1938 Nov 22 13:15 bin
drwxr-xr-x  1 root root  326 Nov 23 18:38 boot
drwxr-xr-x 14 root root 4080 Nov 23 18:43 dev
drwxr-xr-x  1 root root 2820 Nov 23 18:43 etc
drwxr-xr-x  1 root root   26 Nov 22 13:16 home
lrwxrwxrwx  1 root root   32 Nov 22 13:11 initrd.img -> boot/initrd.img-3.5.0-17-generic
lrwxrwxrwx  1 root root   33 Nov 22 13:11 initrd.img.old -> /boot/initrd.img-3.5.0-17-generic
drwxr-xr-x  1 root root  982 Nov 22 13:15 lib
drwxr-xr-x  1 root root   40 Nov 22 13:10 lib64
drwx------  1 root root    0 Nov 22 13:10 lost+found
drwxr-xr-x  1 root root   10 Nov 22 13:10 media
drwxr-xr-x  1 root root    0 Oct  9 17:03 mnt
drwxr-xr-x  1 root root    0 Oct 17 18:22 opt
dr-xr-xr-x 98 root root    0 Nov 23 18:43 proc
drwx------  1 root root   84 Nov 23 18:42 root
drwxr-xr-x 17 root root  620 Nov 23 18:43 run
drwxr-xr-x  1 root root 3094 Nov 23 18:38 sbin
drwxr-xr-x  1 root root    0 Jun 11 20:36 selinux
drwxr-xr-x  1 root root    0 Oct 17 18:22 srv
dr-xr-xr-x 13 root root    0 Nov 23 18:43 sys
drwxrwxrwt  1 root root    0 Nov 23 18:42 tmp
drwxr-xr-x  1 root root   70 Nov 22 13:10 usr
drwxr-xr-x  1 root root  114 Nov 23 18:38 var
lrwxrwxrwx  1 root root   29 Nov 22 13:11 vmlinuz -> boot/vmlinuz-3.5.0-17-generic
lrwxrwxrwx  1 root root   29 Nov 22 13:11 vmlinuz.old -> boot/vmlinuz-3.5.0-17-generic
root@server1:~#


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