# btrfs filesystem df
# btrfs filesystem show
# btrfs filesystem defragment /path
# btrfs filesystem label /path <label>

# btrfs subvolume create <name>
# btrfs subvolume show /path/to/subvolume
# btrfs subvolume list /path
# btrfs subvolume snapshot /old /new
# btrfs sub snap -r /old /.snapshot/ro     # read only