If you need buy a hard drive by yourself, please don't buy hard drive for desktop computer system.
The hard drive for desktop has the word "desktop" in its description.
The hard drive for DVR NVR has the word "surveillance" in its description.
If you know the model of hard drive, search it in google to check it is desktop or surveillance use.
Below are reasons why desktop hard drive can not be used in DVR NVR system.
1. The current to power on desktop hard drive is bigger than surveillance hard drive.
Therefore, if you install desktop hard drive into DVR NVR, DVR NVR may be not able to power on hard drive and make it work.
2. The desktop hard drive is designed for 8 hours everyday use, not for 24 hours every day use.
Therefore, if you install desktop hard drive into DVR NVR, hard drive may be broken after several weeks 24 hours running.