LOTS of new cloud-based CCTV providers are out there....they just charge a flat fee per camera, per month, etc.

Many of the simple little Linux-based DVRs from Swann, Lorex, or similar companies are pretty much set and forget. As long as the drive keeps spinning and the power supply keeps humming, the device is capturing video.

IP-based video cameras are just another device on the network, and the IP-based NVRs are just servers.

Most, if not all Security DVRs simply overwrite at a certain threshold. Typically when the disks get to something like 90% full, they begin over-writing oldest data.