How to fix drive locking (not recognised) on Synology
WARNING: Follow these steps at your own risk.
Enable SSH on the Synology and log in with your admin account, then type:
and type in your password.
Navigate to the folder where the drive list is stored.
edit *_host.db and *_host.db.new and add your drive. In our case we had to add this line to the DB rs2821rp+_host.db and rs2821rp+_host.db.new