1. What eats space
Three things use storage: resolution, camera count and frame rate (fps). Higher resolution and more fps mean bigger files. Compression shrinks them — H.265 keeps the same quality on half the space of H.264.
2. How long footage lasts
Recording non-stop fills storage constantly. A 30-day retention needs a bigger disk than 7 days. If cameras record only on motion, storage lasts longer.
3. What is realistic
For most sites, 15 to 30 days is enough. Incidents are usually noticed in that window. More than 30 days makes sense for sites with long procedures, like disputed claims.
4. How it is calculated
Camera count times resolution times fps gives the amount per day. Multiply by days and you get the needed disk size. The calculator does it for you.
5. Why retention is agreed
With monitoring, the retention period is agreed. It is not a technical value, but an agreement on how long footage stays available — and who accesses it.
6. When a disk fails
A disk is invisible until it fails. That is why regular checks are part of a service agreement. Disk health is tracked, and replacement is planned before footage disappears.
7. Recommendation
Start from the need, not the disk. Decide how many days you need, then calculate the disk. A disk is cheaper than lost footage.
RULE OF THUMB: Retention first, disk after. The reverse leads to footage that disappears before it is needed.