How to size CCTV storage retention without guessing.

Most CCTV storage shortfalls trace back to one mistake: retention was assumed rather than calculated. A system installed with default settings might promise “30 days of storage,” but that number depends entirely on variables that change from site to site.

The variables that actually matter

Camera count and resolution. More cameras and higher resolution both increase the data generated per hour. A 4MP camera can produce roughly four times the data of a 1080p camera at the same frame rate.

Frame rate. Recording at 15fps instead of 30fps can roughly halve storage consumption with minimal impact on usability for most general-purpose coverage — though fast-moving areas may need the higher rate.

Codec. Modern codecs such as H.265 typically use less than half the storage of H.264 for comparable quality, which is one of the simplest ways to extend retention without adding disks.

Motion-based recording. Recording only on motion, rather than continuously, can dramatically reduce storage needs in low-traffic areas — but continuous recording is usually still required for entrances, tills and other high-priority zones.

Retention policy. The number of days you actually need to retain footage should be decided first, based on how quickly an incident is typically reported and reviewed, not backed into from whatever storage happens to be installed.

Working it out properly

A proper sizing exercise starts from the retention policy you need, works out the daily storage generated per camera at the chosen resolution, frame rate and codec, and only then sizes the disk array — with headroom for growth and disk redundancy.

Skipping this step is how sites end up discovering, after an incident, that the footage they needed was already overwritten. It is one of the first things worth checking in any CCTV audit.