Seagate Skyhawk 4TB 7200 RPM Surveillance 3.5 Inch SATA Desktop Internal Hard Disk Drive ( ST4000VX013 )

WD Purple 6TB 5400 RPM 3.5-Inch SATA Surveillance Hard Disk Drive ( WD64PURZ )

WD Purple drives are designed to meet the challenges of 24×7 video surveillance recording. These drives are engineered specifically for surveillance to help withstand the elevated heat fluctuations and equipment vibrations within NVR environments. An average desktop drive is built to run for only short intervals, not the harsh 24/7 always-on environment of a high-definition surveillance system. With WD Purple drives, you get reliable, surveillance-class storage that’s tested for compatibility in a wide range of security systems. Exclusive All Frame technology helps reduce frame loss and improve overall video playback.