WD Purple 2TB Surveillance... Price $96.80 WD Purple 3TB Surveillance... Price $132.00 WD Purple 4TB Surveillance... Price $171.60 Engineered specifically for surveillance security systems. Supports up to 180TB/year workload rate. Tuned for write-intensive, low bit-rate, high stream-count applications typical to most surveillance applications. Prioritized write-operations for maximized surveillance performance. TLER & ATA streaming support. Support for more than eight bays.