WD Purple 8TB Surveillance Hard Drive 5400RPM SATA 256MB Cache 3.5"Western Digital WD Purple 8TB Surveillance Hard Drive 5400RPM SATA 256MB Cache 3. 5" The WD Purple WD85PURZ is an 8TB surveillance class hard drive engineered for 24 7 video recording in high definition security systems. Designed to handle the demands of continuous operation, this drive features AllFrame 4K technology, 256MB cache, and a 180TB year workload rating to ensure reliable performance in multi camera NVR and DVR environments. Engineered for