NAS vs DAS vs SAN (Storage Architectures)

Overview

Storage systems are not defined solely by disks or RAID configuration.
The way storage is connected and accessed is equally important.

The three primary storage architectures are:

• DAS (Direct Attached Storage)
• NAS (Network Attached Storage)
• SAN (Storage Area Network)

Each has different characteristics in terms of:

• Performance
• Scalability
• Complexity
• Suitability for specific applications (including CCTV systems)

DAS (Direct Attached Storage)

Definition

DAS is storage that is directly connected to a single system, typically via:

• SATA
• SAS
• USB (consumer level)

The storage is not shared over a network.

Characteristics

• Simple architecture
• Low latency
• No network dependency
• Limited scalability
• Typically managed by the host system

Advantages

• High performance (direct connection)
• Low complexity
• Cost-effective
• No network overhead

Disadvantages

• Not easily shared between systems
• Limited expansion without hardware changes
• Single point of failure (host system)

Use in CCTV Systems

Most NVRs use DAS internally:

• Internal drive bays
• Direct SATA/SAS connections
• RAID implemented within the recorder

Typical use:

• Small to medium CCTV systems
• Standalone NVR deployments

NAS (Network Attached Storage)

Definition

NAS is a storage system connected to a network and accessed via file-level protocols such as:

• SMB (Windows shares)
• NFS

Characteristics

• Centralised storage
• File-level access
• Accessible by multiple systems
• Runs its own operating system

Advantages

• Easy to deploy and manage
• Shared storage across multiple devices
• Scalable (within platform limits)
• Cost-effective compared to SAN

Disadvantages

• Network dependent
• Higher latency than DAS
• Limited performance under heavy write loads
• Not ideal for high-throughput continuous recording

Use in CCTV Systems

NAS is sometimes used for:

• Archive storage
• Secondary recording targets
• Export / backup

Limitations:

• May struggle with high camera counts
• Performance depends heavily on network bandwidth

SAN (Storage Area Network)

Definition

SAN is a high-performance storage network that provides block-level access to storage devices.

Typically uses:

• Fibre Channel
• iSCSI (over IP networks)

Characteristics

• Appears as local disks to the host
• High throughput and low latency
• Designed for enterprise workloads

Advantages

• High performance
• Scalable
• Suitable for critical systems
• Supports large storage arrays

Disadvantages

• High cost
• Complex design and management
• Requires specialised knowledge

Use in CCTV Systems

SAN is used in:

• Large-scale VMS deployments
• Multi-server recording systems
• Critical infrastructure environments

Comparison Overview

Block vs File Storage (Key Concept)

• DAS / SAN → Block-level storage

  • Appears as raw disks
  • Managed by the host system

• NAS → File-level storage

  • Accessed via network shares
  • Managed by the NAS OS

Network Considerations

For NAS and SAN systems:

• Network bandwidth is critical
• Latency directly affects performance
• Poor network design can result in:
  • Dropped frames
  • Recording gaps
  • System instability

CCTV Design Considerations

Small Systems

• DAS (internal NVR storage) is typically sufficient

Medium Systems

• DAS or hybrid DAS + NAS
• Consider network limitations

Large Systems

• SAN or distributed storage
• Multiple recording servers
• Dedicated storage infrastructure

Common Mistakes

1. Using NAS for High-Throughput Recording

NAS systems may not handle sustained write loads required for large CCTV systems.

2. Ignoring Network Bottlenecks

Bandwidth limitations can reduce effective storage performance.

3. Overcomplicating Small Systems

Using SAN for small installations adds unnecessary cost and complexity.

4. Assuming All Storage is Equivalent

Connection type significantly impacts system behaviour and reliability.

Practical Guidance

• Use DAS for most standalone CCTV systems
• Use NAS for archive or secondary storage
• Use SAN for large or critical deployments
• Always validate performance against:
  • Camera count
  • Bitrate
  • Retention requirements

Related Topics

• RAID (Redundant Array of Independent Disks)
• Disk Types (HDD vs SSD vs Surveillance Drives)
• Storage in CCTV Systems
• CCTV Storage Calculator

Summary

Storage architecture determines how data is accessed and managed.

• DAS is simple and performant for standalone systems
• NAS provides shared storage with moderate performance
• SAN enables high-performance, scalable storage for enterprise systems

Correct selection depends on:

• System size
• Performance requirements
• Operational complexity