How much storage do 8 cameras need? Calculation and drive choice

Eight cameras recording continuously for thirty days need roughly 5 TB at 2 MP and 11 TB at 4 MP. The calculation is one line: number of cameras, daily data per camera, number of days. The rest is choosing these three numbers correctly.

The formula

cameras × daily GB × days ÷ 1000 = TB. The number of cameras and days comes from the job; the daily data volume depends on the scene, so we work with a planning value. Our storage calculator assumes H.265 and a bitrate of 2048 kb/s at 2 MP and 4096 kb/s at 4 MP, which is about 22.1 GB at 2 MP and about 44.2 GB at 4 MP per camera per day. This is an estimate, not an on-site measurement.

Why “about”? Because the encoder works according to the picture. A camera facing an empty warehouse wall writes less, a busy entrance gate more. “About” here is not caution, it is the information that the figure depends on the scene, so you have to allow headroom.

“How many TB” is half the question

The other half: does the drive fit in the recorder? It is not a question of whether it can cope, but of the manufacturer stating what drive size the unit supports and how many drive bays it has. Check this on the datasheet of the recorder you choose. If the calculation goes above the per-bay limit, the answer is not a larger drive but more bays, a larger recorder or fewer retention days.

That is why it is worth deciding on the drive and the recorder together, not one after the other. You cannot add a drive bay to a finished system later.

Motion-triggered recording: less data, but not predictable

Motion-triggered recording produces less data, there is no arguing with that. What cannot be said in advance is how much less, because it depends on the scene: how much pedestrian and car traffic there is, how bright the street light is at night, whether there is a moving branch or flag in the picture, and how much of the street is in view.

That is why we do not promise days for it, and you should not either. What you can do: start the system with continuous recording; after a week the recorder shows the actual daily data volume, and from there retention can be calculated exactly. That one week is worth more than any table.

Overestimating and underestimating

Overestimating shows in the price of the drive, and that is all. Annoying, but nobody notices.

Underestimating, however, comes out exactly when the system has to be used: the customer looks for last month's event, and it has already been overwritten. That means a return trip to the site, explanations, and in the worst case a warranty dispute. The two errors are not equal: better one drive size too big.

What to put in the quote

The customer is not buying TB, they are buying days. Put the retention days, the resolution, the recording mode and the drive size in the quote, in one line:

8 × 4 MP cameras, continuous recording, 8 TB drive, giving about 22 days of retention.

That way the customer knows what they get, and if they want more, it becomes a matter for the quote, not a complaint.

Which hard drive belongs in the recorder

First check the number of drive bays and the supported capacity on the recorder datasheet; then choose a surveillance drive built for continuous writing, not a desktop one: the recorder writes around the clock, several camera streams at once. In our range these are the WD Purple and Seagate SkyHawk families; sizes and specifications are on the product pages.

Round the TB from the formula up to the next factory size, and check that the recorder supports it. The full range: hard drives.

Summary