Comment # 2 on bug 1102142 from Mikhail Kasimov

4) # btrfs fi show /dev/sda2
Label: none  uuid: ca9f936a-0dc2-497b-9192-3b69fee69831
    Total devices 1 FS bytes used 7.97GiB
    devid    1 size 8.55GiB used 8.55GiB path /dev/sda2