Build an auditable storage estimate from bitrate, recording schedule, retention and usable capacity—then add operational headroom without hiding assumptions.
Section 01
Storage starts with assumptions, not disk bays
A useful storage calculation records the number of streams, average planning bitrate for each stream, recording hours per day, expected activity if event recording is used, retention days and the difference between raw and usable capacity. Resolution matters, but it is not a storage value by itself. Codec, frame rate, scene motion, noise, exposure and quality settings all affect the resulting bitrate.
When the exact camera profile is unknown, create a conservative planning scenario and label it. During commissioning, measure representative scenes—including busy and low-light periods—and revise the estimate before the final retention acceptance test.
Section 02
Use one transparent base formula
For continuous recording, start with aggregate average bitrate. Storage in bytes equals total bits per second multiplied by recording seconds, then divided by eight. For a multi-day estimate, multiply by the number of recording hours per day and retention days. Convert consistently to decimal terabytes or tebibytes and state which convention the worksheet uses.
For example, an assumed aggregate stream of 64 megabits per second recorded continuously for 30 days is approximately 20.7 decimal terabytes before filesystem overhead, protection, spare capacity or bitrate variation. This is an engineering estimate, not a guarantee: the actual streams must be measured with the intended camera profiles and scenes.
| Input | Unit | Source |
|---|---|---|
| Camera streams | count | Approved camera schedule |
| Planning bitrate | Mb/s per profile | Camera configuration or measured sample |
| Recording schedule | hours/day or activity factor | Security operating requirement |
| Retention | days | Client policy or regulatory requirement |
| Usable capacity factor | system-specific | Recorder/array design and current documentation |
| Reserve | project decision | Growth and operational tolerance |
Section 03
Separate raw capacity from usable retention capacity
Adding the labels on installed drives gives raw capacity. The capacity available for recordings can be lower after formatting, reserved space, array protection or recorder-specific storage management. A quotation should therefore state drive quantity and nominal size, expected usable basis, protection mode if any, and the retention scenario used for the estimate.
Redundancy and retention solve different problems. Protection may improve tolerance to a drive failure, but it consumes capacity and does not replace backups or evidence-export procedures. Confirm what happens during a failed-drive rebuild and whether recording performance or retention changes.
- Confirm compatible surveillance-drive models and supported maximum capacity
- Confirm the number of installed and available bays
- Document RAID or protection behavior where supported
- Reserve room for bitrate peaks, database overhead and planned additions
- Test playback and export while the system is recording at the design load
Section 04
Validate retention after commissioning
The design calculation becomes credible only when it is checked against operating data. After camera profiles, schedules and scene views are stable, record average and peak bitrate samples. Compare the oldest available video date with the required retention and repeat the check after a representative busy period.
Also verify that time settings are correct, event recording triggers behave as documented and operators can export evidence without interrupting recording. Keep the final worksheet with the as-built configuration so later camera additions are evaluated against the remaining bandwidth and storage margin.
Engineering references
These sources support the general planning principles. Always use the selected product's current datasheet and applicable project standards for final design.
