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

btrfs subv set-default 258 /path
mount -o subvol=/subv/0/vol0 /dev/sdb1 /path

• https://en.opensuse.org/SDB:BTRFS
• https://btrfs.wiki.kernel.org/index.php/Status