When setting up a surveillance system, one of the most critical decisions you’ll make is selecting the appropriate storage size for your Network Video Recorder (NVR). Whether you're working on a small home installation or a large commercial setup, understanding how camera resolution, number of channels, and recording preferences affect storage requirements is key to ensuring reliable and long-term video retention.
Understanding Camera Resolution and Channels
The total amount of storage your NVR needs is directly influenced by two primary factors: the resolution of each camera and the total number of cameras in the system.
Camera resolution is typically measured in megapixels (MP). Common options include:
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2MP (1080p): Standard Full HD resolution.
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4MP: Sharper than 1080p and commonly used in modern systems.
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8MP (4K): Ultra High Definition with a much larger file size.
A higher resolution camera produces clearer, more detailed footage, but it also generates larger video files. For example, an 8MP camera will consume more storage per minute of footage than a 2MP camera under the same conditions.
The number of channels on your NVR refers to how many cameras it can support. More cameras mean more simultaneous video streams being recorded, which increases the overall storage requirement.
Recording Modes: Continuous vs. Motion-Based
Another significant factor in determining storage needs is the recording mode. Most NVRs offer at least two primary modes:
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Continuous Recording: The NVR records video 24 hours a day, regardless of whether there is any motion. This mode is best for high-security areas where uninterrupted footage is crucial, but it requires significantly more storage.
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Motion-Only Recording: The NVR records only when motion is detected. This approach can dramatically reduce the required storage, particularly in low-traffic areas or during nighttime when activity is minimal.
For example, if a motion-only camera records just 20% of the time, it will use approximately one-fifth of the storage compared to a continuously recording camera.
How to Estimate Storage Requirements
To calculate the estimated storage required for an NVR system, you can use the following formula:
Storage (in GB) = Bitrate (Mbps) × 3600 × 24 × Days × Number of Cameras ÷ 8 ÷ 1024
Here's what each variable represents:
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Bitrate: The data rate for each camera, typically between 2 Mbps and 8 Mbps depending on resolution and compression.
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3600 × 24: Converts the bitrate into daily usage (in seconds per day).
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Days: The number of days of video you want to retain.
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Number of Cameras: Total number of channels recording to the NVR.
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÷ 8: Converts bits to bytes.
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÷ 1024: Converts megabytes to gigabytes.
Let’s go through a couple of example scenarios.
Example 1: 8 Cameras, 4MP, Continuous Recording, 30-Day Retention
Suppose you have eight 4MP cameras, each using about 6 Mbps with H.265 compression. You want to retain footage for 30 days, and all cameras are recording continuously.
Using the formula:
Storage = 6 Mbps × 3600 × 24 × 30 × 8 ÷ 8 ÷ 1024
≈ 4,730 GB ≈ 4.7 TB
In this case, you would need at least a 5TB drive. However, it’s wise to plan for some overhead, so a 6TB or 8TB drive would be more appropriate.
Example 2: 16 Cameras, 2MP, Motion-Only Recording (20% of Time), 14-Day Retention
In this scenario, you're using 16 cameras at 2MP each, recording at 3 Mbps. However, you’ve set the system to record only on motion, and motion is detected roughly 20% of the time. You need to retain footage for 14 days.
First, adjust the bitrate to account for motion-only recording:
Adjusted Bitrate = 3 Mbps × 0.2 = 0.6 Mbps
Now, plug into the formula:
Storage = 0.6 Mbps × 3600 × 24 × 14 × 16 ÷ 8 ÷ 1024
≈ 907 GB ≈ 0.9 TB
In this case, a 1TB drive could be sufficient, but opting for 2TB would provide room for flexibility and future needs.
RAID Considerations for Larger Installations
If your NVR setup uses a RAID (Redundant Array of Independent Disks) configuration for data redundancy and uptime, your usable storage will be reduced depending on the RAID level:
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RAID 5 uses one drive’s capacity for parity, so in a 4-drive setup with 4TB drives (16TB total), only 12TB is usable.
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RAID 6 uses two drives for parity, so the same setup would give you 8TB usable.
RAID configurations offer higher reliability and fault tolerance, especially in commercial or mission-critical environments, but they require more total raw storage to achieve the same usable space.
Other Storage Tips
To make the most of your storage and ensure long-term reliability:
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Use H.265 compression if supported. It provides much better storage efficiency than H.264.
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Overprovision by 10–20% to account for indexing, system use, and future scalability.
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Choose surveillance-grade hard drives, such as WD Purple or Seagate SkyHawk, which are designed for 24/7 write-intensive workloads.
Final Thoughts
Selecting the right hard drive or RAID volume size for your NVR depends on understanding your system’s camera resolution, number of channels, recording settings, and retention goals. With the right calculations and a bit of foresight, you can ensure your surveillance system captures and retains the video footage you need—without running out of space at the wrong time.
