the ext4 driver doesn't (in fact, cannot) upgrade file systems missing features. If you mount an ext2 file system from the 1990s with the ext4 driver, it'll sta

the ext4 driver doesn't (in fact, cannot) upgrade file systems missing features. If you mount an ext2 file system from the 1990s with the ext4 driver, it'll stay at the old feature set, for better and worse. You can use tune2fs to upgrade file systems, downgrading is not (usually) possible without a full backup and restore.