The amount of space required for recording on motion for 12 IP cameras will depend on the amount of motion. To make an estimate we can say you will have 25% of the time recorded as motion or 4 ip cameras recorded continuously. Security Monitor Pro records compressed video or 512kb per second which equals 3.8Mb per minute, or 5.5GB per day per camera. A 2TB hard drive will hold approximately 90 days of recordings on motion activation from 12 cameras based on a 25% motion time.