This article was machine-translated from French and is being reviewed. Prices are in Algerian dinars excl. VAT.
The number of recording days is calculated by dividing the hard‑drive capacity by what your cameras record each day. With 4 cameras, 2 MP in H.265 at 2 Mb/s each, a 4‑To disk holds about 46 days. Here is the formula, the bitrates to keep in mind, the effect of H.265 and motion detection, then the disks from the store.
In short
- Formula: days = capacity in GB ÷ (number of cameras × bitrate in Mb/s × 10.8).
- For 4 cameras, 2 MP at 2 Mb/s: 4 × 2 × 10.8 = 86.4 GB per day, i.e., 46.3 days on 4 To.
- In store, the Hikvision 4‑To surveillance disks (28,000 DA HT) and 6‑To (39,500 DA HT) were in stock at the time; the 8‑To (49,000 DA HT) was out of stock.
The calculation of recording days, step by step
- Take the bitrate of a camera in megabits per second (Mb/s). It is set in the recorder, and in the camera itself for an IP camera.
- Convert to GB per day: 1 Mb/s = 0.125 MB/s, and 0.125 × 86,400 s = 10,800 MB = 10.8 GB per day.
- GB per day = number of cameras × bitrate × 10.8.
- Days = disk capacity (GB) ÷ GB per day.
A 4 TB disk sells for 4,000 GB. Your recorder often shows about 3.6 TB: the difference comes from units (the manufacturer counts in powers of 10, the recorder in powers of 2), not from a loss of capacity. Still keep about 10 % margin, as the bitrate varies with the scene and the disk reserves space for its internal management: 4,000 × 0.9 = 3,600 GB, or 3,600 ÷ 86.4 = 41.7 days instead of 46.3.
Which bandwidths to keep?
| Definition | H.264 | H.265 |
|---|---|---|
| 2 MP | 2 to 4 Mb/s | 1 to 2 Mb/s |
| 4 MP | 4 to 6 Mb/s | 2 to 4 Mb/s |
| 5 MP | 5 to 8 Mb/s | 3 to 4 Mb/s |
| 8 MP | 8 to 16 Mb/s | 4 to 8 Mb/s |
These are typical ranges for a standard scene in continuous recording, not guaranteed values: the actual bitrate depends on the scene, lighting, frame rate and quality set on the recorder. Measure it on the installation before fixing disk capacity.
Example figure: 4 cameras 2 MP in H.265
At 2 Mb/s per camera: 4 × 2 × 10.8 = 86.4 GB per day.
| Disk | Capacity | Days (capacity ÷ 86.4) |
|---|---|---|
| 3 TB | 3,000 GB | 34,7 |
| 4 TB | 4,000 GB | 46,3 |
| 6 TB | 6,000 GB | 69,4 |
| 8 TB | 8,000 GB | 92,6 |
With 8 cameras, the need doubles: 8 × 2 × 10.8 = 172.8 GB per day. A 4 TB disk then holds 4,000 ÷ 172.8 = 23.1 days, and an 8 TB disk 46.3 days.
What changes the duration
- H.265 vs H.264: at 4 Mb/s in H.264, the same 4 cameras produce 4 × 4 × 10.8 = 172.8 GB per day, i.e., 4,000 ÷ 172.8 = 23.1 days on 4 TB, versus 46.3 in H.265. The real gain depends on the model and scene, and both camera and recorder must support H.265.
- Motion‑based recording: assuming a school, if the scene is active only 25 % of the time, the need drops to 86.4 × 0.25 = 21.6 GB per day, or 4,000 ÷ 21.6 = 185.2 days on 4 TB. The actual activity share varies by site: in a shop open all day, the gain is small.
- Resolution and frames per second: an 8 MP camera or set to 25 fps weighs more than a 2 MP at 12 fps.
Which disk, at what price?
Store price list asloitech.com as of 06/11/2026, subject to availability.
| Disk | Price (DA HT) | Availability | Price per TB |
|---|---|---|---|
| WD surveillance 3 TB (Dahua) | 21 500 | break at the top | 21 500 ÷ 3 ≈ 7 167 |
| Hikvision surveillance 4 TB | 28 000 | in stock | 28 000 ÷ 4 = 7 000 |
| Hikvision surveillance 6 TB | 39 500 | in stock | 39 500 ÷ 6 ≈ 6 583 |
| Toshiba S300 surveillance 6 TB | 41 900 | break at the top | 41 900 ÷ 6 ≈ 6 983 |
| Hikvision surveillance 8 TB | 49 000 | break at the top | 49 000 ÷ 8 = 6 125 |
The price per TB decreases overall with capacity, and the 8 TB drive is cheapest per TB, but it was out of stock at the time of the quote. A 3.5" WD 1 TB disk is in stock for 8,500 DA excl. VAT, but its datasheet does not present it as a surveillance disk: a desktop drive is not designed for 24 h/24 writing. For 4 cameras at 86.4 GB per day, it only holds 1,000 ÷ 86.4 = 11.6 days.
Also check the maximum capacity your recorder accepts. According to Dahua datasheets, Cooper XVRs are limited to 6 TB per disk (an 8 TB does not fit), whereas recent XVR i3 datasheets announce up to 16 TB.
To size the whole system, see how to choose your installation. The disk cost is included in the price of a coaxial installation.
Frequently asked questions
Is a PC disk suitable for CCTV?
It works, but it is not designed to write continuously 24 h/24. The “surveillance” disks are meant for continuous writing and to receive multiple video streams at once.
What happens when the disk is full?
The recorder usually erases the oldest sequences to write new ones (overwrite), a setting available in the recorder’s menu. Export important sequences before they are replaced.
Can multiple disks be installed?
It depends on the recorder: compact 4‑ and 8‑channel models usually have only one slot. In store, the XVR 16‑channel XVR7216AN-4K-I3 is listed as “2HDD” at 140,000 DA HT (in stock), and the NVR 16‑channel NVR5216-EI 4KS2 “2 HDD” at 73,000 DA HT (in stock).
What to do with an old hard drive?
A disk that has recorded images keeps them until it is securely erased. Before discarding, donating or reselling it, have it erased. AsloTech offers secure disk wiping.
A technician can calculate the exact duration for your site and set the recorder: discover our video surveillance CCTV solution or the CCTV category in the store. To compare technologies, read IP or analog camera. The declaration, information and retention obligations are detailed, with their reservations, in your ANPDP obligations.