Purpose

Let’s make a root(/) partition except /boot directory be btrfs. btrfs supports a copy-on-write functionality.

For the reason of excepting /boot partition, the Ubuntu document warns against including Grub into btrfs partition.

… As of 11.04, it is possible to use only btrfs file systems with the caveat that grub ‘MUST NOT’ be installed to the boot sector of the btrfs volume containing /boot.
(link)

As a result, I decided to make the /boot partition be separated from the root(/) partition.

Prerequisites

• Live bootable USB or Live CD of Ubuntu (refer to link: Making Live bootable USB)

• Make boot partition be separated from your btrfs partition. (refer to link: Create boot partition after installation)

• Grub Legacy (not Grub2. Refer to link: Downgrade Grub2 to Grub Legacy)

Reference

Basically, refer to the link for a whole process. This article is just for supporting the referenced site.

Problems & Solutions

Booting with Live USB

During the process, you need to umount the directory to be converted to btrfs. In this article, we are converting the whole root partition, so it is required to be booted with Live USB. Otherwise, you will fail to command btrfs-convert, being prompted something like: /dev/sda1 is mounted.

Cannot install btrfs-tools in Lively booted system

You might fail to install btrfs-tools because apt-get cannot find the package from repositories. Including all the repository will resolve this problem.

1. Go to Application > Ubuntu Software Center

2. From menu, Edit > Software Sources

3. Check all the list in Download from the Internet

4. Retry apt-get install btrfs-tools

Updated

It is recommended to use an updated version of btrfs-tools. You can get btrfs-tools_0.19+20100601-3ubuntu3_amd64.deb from link and install as below.

sudo dpkg -i btrfs-tools_0.19+20100601-3ubuntu3_amd64.deb

Without this updated tool, you cannot delete snapshot of btrfs.

Success of btrfs-convert

If you succeeded in btrfs-convert, the following messages will be prompted.

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

Change UUID in menu.lst file

With Grub Legacy we need to modify root=UUID value in menu.lst file to btrfs partition’s manually. I used the following lines for Grub’s menu.lst file.

title       Linux 2.6.32.67
uuid        89591593-766e-4565-9d5c-017fb0e33298
kernel      /vmlinuz-2.6.32.67 root=UUID=a90c79b1-5883-44cc-9e74-752db9ca764d ro
initrd      /initrd.img-2.6.32.67

In this example, a90c79b1-5883-44cc-9e74-752db9ca764d is the UUID of btrfs partition and 89591593-766e-4565-9d5c-017fb0e33298 is UUID of /boot partition.

Also, I used following lines for my /etc/fstab file.

/dev/sda3       /boot       ext4     defaults       0       0   
/dev/sda1       /           btrfs    defaults        0       1

As you can see, I just wrote a path (/dev/sda1) instead of UUID as described in the referenced site.

Update initrd images

Because some scripts and hooking are added to initramfs, initrd images in /boot directory should be updated.

I could not update them with command (i.e. update-initramfs -u -k all) described in the referenced site. It was guessed due to the kernel version difference between Live USB and my original installation. I designated the kernel version as a parameter like below and it worked.

update-initramfs -u -k 2.6.32.67

Good luck! :)