The technical starting position
Four cameras with continuous high quality fill storage differently than four cameras that only record relevant events. Also a change in bitrate or an additional camera changes the outcome.
advice
Calculate NVR storage capacity
Storage capacity is a calculation that starts with what you want to be able to find later, not with the biggest hard drive that fits in a recorder.
What you calculate or measure
Note the resolution, frames, bitrate, recording plan, and desired storage duration for each channel. Compare that requirement with the actual usable disk space and any potential growth.
The intervention that fits
Choose storage based on the established principles and allow room for change where it is reasonable. Do not simply reduce all quality to hide a capacity shortfall.
Proof that it works
After a few days, check the oldest available recording and compare it with the calculated expectation. Update the calculation when settings or the number of cameras change.
Frequently asked questions
How many days can I look back?
That depends on the cameras, settings, activity and available storage.
Is an event recording always much smaller?
Not necessarily; a lot of activity or broad detection zones can still provide a lot of data.