Seagate SkyHawk, 4 TB, Surveillance Internal Hard Drive HDD 3.5 Inch SATA 6 Gb/s 64 MB Cache for DVR NVR Security Camera System, and Three year Rescue Services, Silver (ST4000XV007)

Amazon

ImagePerfect firmware NVR-ready design ATA streaming support 1 M hours MTBF, 3-year limited warranty Enjoy long-term peace of mind with the included two-year limited warranty and two-yr Rescue Data Recovery Services

Zoro Tools

- Hard drive suitable for 24/7 use - Fast installation