I ordered and these were all ST3600057SS. We had some expansion bays available in our 8-bay R520 server, so we added these drives and simply created a new RAID so as to avoid any mismatch issues we may have encountered with the existing installed drives in our setup. The drives were recognized right away by the Server and it re-built our RAID 10 array so that it once again regained its health. They are excellent SAS drive for Dell servers.