Well I suppose your answer depends on whether or not these are apple drives. I had this exact same problem and it ended up being a firmware issue with the drive. If they are not apple drives, I would suggest that you find a firmware update from the manufacturer. If they are apple drives, you may need to switch to a new media type as you probably won't be seeing a firmware update from apple anytime soon. Although you can just use the firmware from the OEM if you are not concerned about a warranty.