df out of space

peter:~ # df -h
Filesystem               Size  Used Avail Use% Mounted on
rootfs                    80G   66G   13G  85% /
devtmpfs                 7.6G   52K  7.6G   1% /dev
tmpfs                    7.9G  2.7M  7.9G   1% /dev/shm
tmpfs                    7.9G  900K  7.9G   1% /run
/dev/sdb3                 80G   66G   13G  85% /
tmpfs                    7.9G     0  7.9G   0% /sys/fs/cgroup
tmpfs                    7.9G  900K  7.9G   1% /var/run
tmpfs                    7.9G  900K  7.9G   1% /var/lock
tmpfs                    7.9G     0  7.9G   0% /media
/dev/mapper/data-backup  200G  163G   36G  83% /backup
/dev/md0                 509M  233M  251M  49% /boot

ipeter:~ # btrfs fi show
failed to read /dev/sr0
Label: none  uuid: 1e74b3ab-ee49-4741-9efb-ef1759459aa7
        Total devices 1 FS bytes used 62.56GiB
        devid    1 size 80.00GiB used 80.00GiB path /dev/sdb3

Btrfs v0.19+20120406

peter:~ # btrfs fi df /
Data:          total=71.97GiB, used=59.56GiB
System, DUP:   total= 8.00MiB, used=16.00KiB
System:        total= 4.00MiB, used= 0.00
Metadata, DUP: total= 4.00GiB, used= 3.00GiB
Metadata:      total= 8.00MiB, used= 0.00


======================================================

peter:~ # btrfs device add /dev/sda3 /
peter:~ # btrfs device add /dev/sdd3 /
peter:~ # btrfs device add /dev/sdc3 /

peter:~ # df -h
Filesystem               Size  Used Avail Use% Mounted on
rootfs                   320G   66G  247G  22% /
devtmpfs                 7.6G   52K  7.6G   1% /dev
tmpfs                    7.9G  2.7M  7.9G   1% /dev/shm
tmpfs                    7.9G  900K  7.9G   1% /run
/dev/sdb3                320G   66G  247G  22% /
tmpfs                    7.9G     0  7.9G   0% /sys/fs/cgroup
tmpfs                    7.9G  900K  7.9G   1% /var/run
tmpfs                    7.9G  900K  7.9G   1% /var/lock
tmpfs                    7.9G     0  7.9G   0% /media
/dev/mapper/data-backup  200G  163G   36G  83% /backup
/dev/md0                 509M  233M  251M  49% /boot

peter:~ # btrfs fi show
failed to read /dev/sr0
Label: none  uuid: 1e74b3ab-ee49-4741-9efb-ef1759459aa7
        Total devices 4 FS bytes used 62.57GiB
        devid    2 size 80.00GiB used 3.00GiB path /dev/sda3
        devid    4 size 80.00GiB used 2.00GiB path /dev/sdc3
        devid    1 size 80.00GiB used 80.00GiB path /dev/sdb3
        devid    3 size 80.00GiB used 4.00GiB path /dev/sdd3

Btrfs v0.19+20120406

peter:/usr/src # btrfs fi df /
Data:          total=74.97GiB, used=59.65GiB
System, DUP:   total= 8.00MiB, used=24.00KiB
System:        total= 4.00MiB, used= 0.00
Metadata, DUP: total= 7.00GiB, used= 3.01GiB
Metadata:      total= 8.00MiB, used= 0.00