btrfs check /dev/sda
Checking filesystem on /dev/sda
UUID: fdce5ae5-fd6d-46b9-8056-3ff15ce9fa16
checking extents
checking free space cache
cache and super generation don't match, space cache will be invalidated
checking fs roots
checking csums
checking root refs
found 131072 bytes used err is 0
total csum bytes: 0
total tree bytes: 131072
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 123735
file data blocks allocated: 0
referenced 0