Convert Ext3 to Btrfs

After I make kernel 2.6.35.4 on Oracle Enterprise Linux 5.4 support Btrfs.

# cd /usr/src
# tar jxvf linux-2.6.35.4.tar.bz2
# cd linux-2.6.35.4
# cp /boot/config-2.6.18-164.el5 .config
# make && make modules_install headers_install install
# mkinitrd /boot/initrd-2.6.35.4 2.6.35.4
# reboot

then installed btrfs-progs-0.19 program.

# cat /etc/enterprise-release
Enterprise Linux Enterprise Linux Server release 5.4 (Carthage)

# rpm -q enterprise-release
enterprise-release-5-0.0.20

# uname -a
Linux oel 2.6.35.4 #1 SMP Wed Sep 1 20:37:04 ICT 2010 x86_64 x86_64 x86_64 GNU/Linux

and then tested to convert ext3 to btrfs (read):

# mount | grep /dev/sda6
/dev/sda6 on /data type ext3 (rw)

# ls /data
linux-2.6.35.4.tar.bz2

# umount /data

# fsck.ext3 /dev/sda6
e2fsck 1.39 (29-May-2006)
/data: ...

# btrfs-convert /dev/sda6
creating btrfs metadata.
creating ext2fs image file.
cleaning up system chunk.
conversion complete.

# mount -t btrfs /dev/sda6 /data

# mount | grep /dev/sda6
/dev/sda6 on /data type btrfs (rw)

# ls /data
ext2_saved linux-2.6.35.4.tar.bz2

we will see ext3/4 snapshot (ext2_saved). we can mount loopback for image in snapshot:

# mount -t ext3 -o loop,ro /data/ext2_saved/image /mnt

# ls /mnt
linux-2.6.35.4.tar.bz2

check some command-line:

# btrfs-show
Label: /data uuid: 7721003c-adcb-4706-8238-68946a5e2547
Total devices 1 FS bytes used 8.73GB
devid 1 size 128.79GB used 128.79GB path /dev/sda6

Btrfs Btrfs v0.19

However, if we need to roll back the conversion(we should backup). we can:

# umount /mnt
# umount /data
# btrfs-convert -r /dev/sda6