Why an NVR With a Large Drive Still Does Not Keep 30 Days of Video

Start with the recording requirement

A large drive can overwrite video earlier than expected when the recorded streams consume more space than the proposal assumed. Start with the required cameras, days and recording schedule, then compare the calculation with actual storage use.

A Reddit office-system planner asked for full recording for thirty days and a reduced-frame archive for a much longer period. That is a concrete retention requirement, not evidence that an arbitrary NVR can perform both jobs. The indexed discussion supports defining each archive separately; no forum capacity recommendation is adopted here.

Define the required days, cameras, continuous versus event recording, image needs, and export procedure. Do not reduce quality until a capacity target fits without checking whether the resulting footage still answers the security question.

Source: NVR recommendation: 30 days full recording plus longer reduced archive

Use a transparent estimate

For a constant average recorded bitrate, decimal gigabytes per day are approximately total megabits per second multiplied by 10.8. This follows from 86,400 seconds per day and eight bits per byte. It is a planning calculation, not a guarantee of usable recorder capacity.

Bitrate can change with scene activity, noise and compression settings. Axis’s compression guidance explains why the recorded data rate affects retention. Separately account for formatting, storage reserved by the recorder and redundancy. A drive’s nominal label is not the usable recording allocation.

Source: Axis: surveillance video compression and bitrate

Illustrative calculation: eight cameras

Assume, purely for illustration, eight cameras averaging 4 megabits per second each and recording continuously. Total bitrate is 32 megabits per second. Multiplying by 10.8 gives approximately 345.6 decimal gigabytes per day. Thirty days requires approximately 10.37 decimal terabytes of recorded data before allowance for the recorder’s other capacity constraints.

If the average rises to 6 megabits per second per camera, the same calculation gives approximately 15.55 terabytes for thirty days. Those are assumed rates, not recommended settings or a quote for a specific product. They demonstrate why a drive-size promise without settings is incomplete.

Event recording changes the evidence tradeoff

Recording only detected events can reduce data, but the result depends on activity and whether detection captures the events that matter. Busy scenes, moving foliage, insects, and changing light can increase recordings. A quiet demonstration period is not a reliable predictor for every season.

If the owner needs the moments before an event or wants to investigate something the detector did not recognize, continuous recording may have value. Compare that requirement with storage and budget explicitly rather than silently changing the recording schedule.

Verify retention on the running system

AXIS Camera Station 5 provides a useful documented example: it displays used storage, configured retention and the oldest recording per camera. Its Limited retention setting specifies a maximum number of days, but a full allocation can cause earlier deletion. In this product, the day limit sets a maximum retention age; it does not reserve the capacity needed. Check the selected recorder’s own retention and overwrite controls.

After commissioning, inspect actual storage consumption and the oldest available recordings under representative conditions. Confirm what happens when the drive fills and whether all cameras follow the intended schedule. Test playback and export from more than one camera.

Record the capacity, settings, measured observation period, and remaining uncertainty. If thirty days have not elapsed, say that retention is estimated from observed consumption rather than verified across the full period. A full drive with an old thumbnail does not prove that every required interval is playable.

Source: AXIS Camera Station 5: recording storage, retention and oldest recording

Put it into practice

A decision table to keep handy