What Drives Storage
CCTV storage comes down to one thing: how many bits each camera produces and for how long you keep them. Everything else is detail. The hard part is estimating bitrate, because it shifts with the scene.
Bitrate Factors
| Factor | Effect on Bitrate |
|---|---|
| Resolution | Higher resolution, more data |
| Frame rate | More frames per second, more data |
| Codec | H.265 roughly halves H.264 for similar quality |
| Scene complexity | Movement, foliage, and crowds raise it |
| Lighting and noise | Low light adds noise, which raises it |
| Compression level | Stronger compression lowers it, with quality cost |
A quiet office hallway and a busy loading dock at the same resolution can differ by a wide margin. Manufacturer bitrate calculators give a starting point. Real footage from a similar site gives a better one.
The Storage Formula
The core calculation is straightforward.
Storage = bitrate (Mbps) / 8 x 3600 x hours/day x days x camerasDividing by 8 converts bits to bytes. Multiplying by 3600 converts seconds to hours. The result is in megabytes, so divide by 1,000,000 to reach terabytes. Use continuous recording hours unless you are confident in motion or event recording, which is harder to predict.
CBR vs VBR
Constant bitrate (CBR) holds a steady data rate, which makes storage easy to predict but wastes capacity on quiet scenes and can starve busy ones. Variable bitrate (VBR) follows the scene, which uses less space overall but makes planning harder. Many integrators run VBR with a capped maximum bitrate. That gives the efficiency of VBR with a known worst case for sizing.
RAID and Usable Capacity
Raw drive capacity is not usable capacity. RAID for redundancy costs space. RAID 5 loses one drive of capacity. RAID 6 loses two. Add filesystem overhead and a buffer, and you should plan to fill no more than about 85 percent of usable space. Size the array on usable terabytes after RAID, not on the sum of the drive labels.
A Worked Example
Twenty cameras, 4 MP at 15 fps, H.265, continuous recording, 30 days retained.
| Parameter | Value |
|---|---|
| Per-camera bitrate | 4 Mbps (capped VBR) |
| Bytes per hour | 4 / 8 x 3600 = 1,800 MB |
| Hours per day | 24 |
| Per camera, 30 days | 1,800 x 24 x 30 = 1,296,000 MB ≈ 1.3 TB |
| 20 cameras | ≈ 25.9 TB |
| With RAID 6 and 15% headroom | ≈ 33 to 35 TB usable target |
Round up and add room for growth. Cameras get added, retention gets extended, and nobody wants to rebuild an array a year in.
Retention Policy
Retention is a business and legal decision, not just a storage one. Keep footage long enough to support investigations, but no longer than you have a reason to. Under PIPEDA, personal information should not be kept past the purpose it was collected for. Many Canadian sites land between 30 and 90 days. Confirm any sector or provincial requirements, document the policy, and apply it consistently.
References
Last updated 2026-06-14.