Storage in CCTV Systems (Engineering Guide)

Overview

Storage is a critical component of any CCTV system.

It determines:

• How long footage is retained
• Whether recording remains stable under load
• How the system behaves during failures

Correct storage design requires consideration of:

• Bitrate and retention requirements
• Disk type and reliability
• RAID configuration
• Throughput and system performance
• Storage architecture (DAS, NAS, SAN)

Core Principle

CCTV storage design is not just about capacity.

A system must be designed to ensure:

• Sufficient capacity (retention achieved)
• Sufficient throughput (no dropped frames)
• Sufficient resilience (continues recording during failure)

Storage Requirement (Capacity)

Storage is typically calculated based on:

• Number of cameras
• Bitrate per camera
• Retention period

Simplified Approach

Total Storage ≈ Cameras × Bitrate × Retention Time

However, real systems must also account for:

• Overhead (filesystem, metadata)
• Variable bitrate behaviour (VBR)
• System reserves

Practical Calculation

For accurate sizing, use:

Use the Fire Secure UK CCTV Storage Calculator to estimate recording capacity and retention.

This calculator includes:

• Bitrate-based estimation
• Motion vs continuous recording
• RAID-aware usable capacity
• Retention validation

Bitrate & Recording Behaviour

Continuous Recording

• Constant data rate
• Predictable storage usage
• Higher total storage requirement

Motion / Activity Recording

• Variable data rate
• Dependent on scene activity
• Less predictable storage usage

Codec Impact

Common codecs:

• H.264
• H.265
• Manufacturer-specific variants (H.265+, etc.)

Actual storage usage varies depending on:

• Scene complexity
• Frame rate
• Compression efficiency

Disk Selection

Disk type has a direct impact on reliability.

Recommended

• Surveillance-rated HDDs (e.g. WD Purple, Seagate SkyHawk)
• Enterprise HDDs (for large systems)

Avoid

• Consumer desktop drives
• Low-end SSDs for bulk storage

Key Consideration

CCTV workloads are:

• Continuous
• Write-heavy
• Sequential

Drives must be designed for sustained operation.

RAID in CCTV Systems

RAID is used to provide continued operation during disk failure.

Common RAID Choices

Important Notes

• RAID reduces usable capacity
• RAID introduces rebuild risk
• RAID does not replace backup

Throughput & Performance

Storage systems must support sustained write throughput.

Example

• 32 cameras @ 4 Mbps
  → ~128 Mbps total (~16 MB/s)

Design Considerations

• Allow headroom (20–30%)
• Consider RAID write penalties
• Validate disk throughput capability

Storage Architecture

DAS (Direct Attached Storage)

• Most common in NVRs
• High performance
• Simple design

NAS (Network Storage)

• Used for archive or secondary storage
• Limited by network performance

SAN (Enterprise Storage)

• Used in large-scale systems
• High performance and scalability

Retention Validation

A system may have:

• Sufficient disk capacity
• But insufficient usable storage (after RAID)

or:

• Sufficient storage
• But insufficient throughput

Both must be validated.

Practical Approach

1. Calculate required storage
2. Apply RAID usable capacity
3. Verify retention is achieved
4. Confirm system throughput is sufficient

Common Design Mistakes

1. Designing for Capacity Only

Ignoring throughput leads to unstable systems.

2. Using Raw Capacity Instead of Usable Capacity

RAID reduces available storage.

3. Using Incorrect Disk Types

Consumer drives are not suitable for continuous recording.

4. Ignoring Rebuild Risk

Large RAID 5 arrays are vulnerable during rebuild.

5. Overloading NAS Systems

Network storage may not handle sustained recording loads.

Practical Design Guidance

• Use surveillance-grade drives
• Prefer RAID 6 for larger systems
• Allow capacity and performance headroom
• Validate both storage and throughput
• Keep system design aligned with real-world workload

Related Topics

• RAID (Redundant Array of Independent Disks)
• Disk Types (HDD vs SSD vs Surveillance Drives)
• NAS vs DAS vs SAN
• Throughput & I/O Considerations
• CCTV Storage Calculator

Summary

CCTV storage design requires balancing:

• Capacity
• Performance
• Reliability

A correctly designed system ensures:

• Stable recording
• Achieved retention
• Continued operation during failures

Tools and calculations support this process, but must be combined with:

• Correct disk selection
• Appropriate RAID configuration
• Proper system design principles