Hi...They are the exactly the same.....a Samsung SP2504C (250GB/7200rpm/8M) rev.A... with no jumper settings, went faulty and a Samsung SP2504C (250GB/7200rpm/8M) rev.A... with no jumper settings replaced it!
The replacement was in one of my PC's as a secondary HD and was working prior to using in the Terastation and subsequently I have tested again in the PC and all is well!