There are many factors when trying to determin how much storage you will need for your DVR. The first thing you need to decide is how long you will need to keep stored video before it begins to record over itself. Security DVRs use hard drives to store your recorded video. You will need to decide on the amount of hard drive space you need. One you have decided on the amount of time you want recorded video to remain, then you will need to examine the other factors that influence storage space. Among those are: