Use this tool to see how much space you will need on the hard drive of your DVR to store different variations of capturing video.

This will help you choose what size hard drive you need, and how best to set up your motion detection on each camera.

http://www.supercircuits.com/resources/tools/security-dvr-storage-calculator

NVR Storage Calculator for Network IP Security Cameras

https://www.supercircuits.com/resources/tools/security-nvr-storage-calculator