BTRFS Issues

sudo btrfs balance start -dconvert=single -mconvert=single /media

Remove drive:

sudo btrfs device remove 2

After conversion BTRFS is unmountable. It complains that devices are still missing, even with -o degraded,recovery,ro. Everything was performed with recent 5.9 kernel.

BTRFS error (device sdb): super_num_devices 2 mismatch with num_devices 1 found here
BTRFS error (device sdc): failed to read chunk tree: -22

Solution:

• https://www.mattzone.com/btrfs/btrfs_20171205.html
• Source code of fix-dev.count.c fix-dev-count.c.gz

References:

• How to recover from BTRFS errors
• Btrfs unmountable - claims it is missing a volume
• btrfs partition is suddenly unmountable [SOLVED don't use btrfs]
• You mostly don't need fsck on btrfs