Btrfs have (had?) interesting failure mode for this scenario, because this is Copy On Write file system it need to allocate new block to modify metadata, when y

Btrfs have (had?) interesting failure mode for this scenario, because this is Copy On Write file system it need to allocate new block to modify metadata, when you are out of space, you cannot do that anymore. You might end up in scenario where your filesystem is full but you cannot delete anything because this required allocating new metadata block and your drive is full