WD WD121PURP 12TB WD Purple Pro Surveillance Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, 256 MB Cache, 3.5 in. With an MTBF of up to 2.5 million hours3 (12TB, 14TB, and 18TB1), WD Purple™ Pro drives are engineered for advanced smart video solutions that operate 24/7.