ext4migrate boot option if you wish to convert your legacy ext3 partitions to ext4. Users are cautioned that they will not realize many of the benefits ext4 since the data currently residing on the partition will not make use of extents. New data will make use of extents. Please note that as suggested by the requirement to pass a boot option that migration to ext4 has not been heavily tested and users are urged to backup filesystems before attempting migration
icantbelieveitsnotbtr as a boot potion. Users are warned that btrfs is still experimental and under heavy development. The on-disk format may yet change and much functionality is still missing such as a fully operative fsck or even proper out-of-space handling.