In short: for a recorder, use a dedicated surveillance series - WD Purple or Seagate SkyHawk. They are built for 24/7 recording, have firmware for multi-stream writes and use CMR. Work out the capacity from the number of cameras, their bitrate and how many days of footage you need to keep.
Why a regular drive is wrong for a recorder
A recorder writes video non-stop, day and night, from several cameras at once. A desktop drive is designed for a different pattern: a few hours a day and mostly reads. In a recorder it runs outside its design limits, overheats in an enclosed box and wears out faster.
Surveillance series differ in three ways:
- Streaming firmware. The drive prioritises uninterrupted writing over response time. If a frame is not written perfectly, it does not stall the stream with retries, so the video does not break up.
- 24/7 operation and a higher annual workload than desktop models.
- CMR recording. Continuous writing is the worst case for SMR; see CMR vs SMR.
WD Purple or Seagate SkyHawk
Both series do the same job and are compatible with popular Hikvision, Dahua and other recorders. Both support up to 64 cameras per drive and multi-drive recorders. The differences are in the details: cache size of a specific model, proprietary technologies (AllFrame from WD, ImagePerfect from Seagate) and the price at the time of purchase. In practice, pick whichever is cheaper at the capacity you need, and avoid mixing different series in one RAID array without reason.
For recorders with video analytics there are separate lines (SkyHawk AI, WD Purple Pro) rated for heavier loads. For a home system with 4-16 cameras, the standard series are enough.
How to calculate the capacity you need
Archive size depends on the camera bitrate. The formula for one camera per day:
bitrate (Mbit/s) × 86,400 s ÷ 8 = megabytes per day
Example: a 2 MP camera with H.265 averages about 2 Mbit/s. That is 2 × 86,400 ÷ 8 = 21,600 MB, or about 21.6 GB per day. Then multiply by the number of cameras and days:
| Cameras | Bitrate | 7 days | 14 days | 30 days |
|---|---|---|---|---|
| 4 | 2 Mbit/s | ~0.6 TB | ~1.2 TB | ~2.6 TB |
| 8 | 2 Mbit/s | ~1.2 TB | ~2.4 TB | ~5.2 TB |
| 8 | 4 Mbit/s | ~2.4 TB | ~4.8 TB | ~10.4 TB |
| 16 | 2 Mbit/s | ~2.4 TB | ~4.8 TB | ~10.4 TB |
This assumes 24/7 recording. With motion-triggered recording the real figure is lower, but do not size it too tight: at night sensor noise and rain trigger the detector and the archive grows. Allow 20-30 % headroom.
Check your cameras' actual bitrate in the recorder settings: it depends on resolution, codec, frame rate and the scene.
Most popular capacities
- 1-2 TB - a house or flat, 2-4 cameras, 1-2 weeks of footage.
- 4 TB - the most common choice for 8 cameras and 2-3 weeks of footage.
- 6-8 TB - office, shop or warehouse, 8-16 cameras or a one-month retention requirement.
All these sizes are in the surveillance drives section and in the 2 TB, 4 TB, 6 TB and 8 TB and larger filters.
What to watch during installation
- Compatibility. Check the recorder documentation for the maximum drive size and number of SATA ports.
- Power. A recorder without a UPS is the biggest risk to both the drive and the footage. When the power goes out, recording stops abruptly and the file system can be damaged.
- Temperature. Do not hide the recorder in a closed cabinet without ventilation. Long periods above 50 °C shorten drive life; see How long does a hard drive last.
- Formatting. Format a new drive from the recorder itself, not on a computer.
- Health checks. Most recorders show drive status and SMART in their menu. Check it at least once a month.
