From btrfs Wiki
This tool can convert ext2 to Btrfs. For a greater detail of how the algorithm works, please see the Conversion from Ext3 page.
btrfs-convert [-d] [-i] [-n] [-r] <device>
Description of parameters
- -d disable computing data checksums, this will speed up the operation
- -i ignore xattrs and ACLs
- -n disable packing of small files
- -r roll back to ext2/3/4 filesystem
The original filesystem image is accessible as from separate subvolume named ext2_subvol as file image.