You can use the btrfs-convert utility to convert an ext file system to a Btrfs file system. The utility preserves an image of the original file system in a snapshot named extN_saved, such as ext4_saved. With this snapshot, you can roll back the conversion, even if you have changed the btrfs file system.

Note that you can't convert a root file system or a bootable partition, such as /boot, to Btrfs.