btrfs - No space left on device

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Environment

SUSE Linux Enterprise Server 12 Service Pack 1 (SLES 12 SP1)

Situation

The device shows less space used on total while on device all space is used:

btrfs fi show /
Label: none  uuid: 57c03625-0299-4173-8cf0-c30338e89798
        Total devices 1 FS bytes used 5.46GiB
        devid    1 size 7.03GiB used 7.03GiB path /dev/<btrfs-device>

Also command "df " shows free space.

Resolution

Boot into rescue system:

mount /dev/<btrfs-device> /mnt

btrfs balance start /mnt/fulldisk

If there is not enough space to balance add an empty disk to btrfs:

btrfs device add /dev/<empty-disk> /mnt

btrfs balance start /mnt

Btrfs filesystem is raid based. To be able to remove second disk again remove raid configuration, otherwise you would see message like:

error removing the device '/dev/<empty-device>' - unable to go below two devices on raid1

run:

btrfs balance start -f -dconvert=single -mconvert=single /mnt

Afterwards the btrfs should show free disk space again:

btrfs fi show /
Label: none  uuid: 57c03625-0299-4173-8cf0-c30338e89798
        Total devices 1 FS bytes used 5.46GiB
        devid    1 size 7.03GiB used 6.34GiB path /dev/<btrfs-device>

Cause

Meta data has exhausted available space.

Disclaimer

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