Retention is a system setting
Storage depends on how many cameras record, how much detail they capture, the frame rate, compression, image complexity, motion, and whether recording is continuous or event-based.
Plan with operating reserve
- Choose a target number of days.
- Use realistic camera settings.
- Include future cameras.
- Leave reserve instead of sizing to a perfect laboratory estimate.
Verify after installation
The Plan a System calculator produces a planning estimate. Actual retention should be checked after the cameras have operated in their real scenes.
A transparent continuous-recording example
For decimal terabytes, estimate: cameras × average megabits per second × 86,400 seconds per day × days ÷ 8 ÷ 1,000,000. Eight cameras averaging 4 Mbps each for 30 days require approximately 10.368 TB of video data before filesystem overhead, reserves or other storage needs. This is an illustrative calculation, not a guaranteed retention promise.
Use the average recorded bitrate, not a camera's Ethernet link speed. Variable-bitrate recording changes with scene detail, motion and noise. If the recorder stores extra streams or audio, include those too. A measured sample from the installed system is more useful than assuming one bitrate fits every scene.
Select capacity and verify retention
A retention target should describe the evidence you need to keep and how it will be retrieved. Reducing frame rate or bitrate may extend retention but also changes the recorded evidence. Decide with sample playback before applying a setting across the whole system.
- Check the NVR's supported drive count, per-drive limits and approved drive requirements.
- Confirm whether the product includes a hard drive; do not assume it does.
- Leave room for overhead and variation rather than selecting exactly the calculated minimum.
- Treat motion-only savings as an estimate until the actual scene has been measured.
- After a full recording cycle, check the earliest available footage and test event export.
Frequently asked questions
Will a certain drive size always keep thirty days?
No. Camera count, actual bitrate, recording schedule, audio, overhead and scene activity determine retention. Verify it on the installed system.
Does motion recording guarantee large storage savings?
No. Busy scenes, weather and settings can keep recording active. Estimate conservatively and measure actual retention.