The three terms describe different storage architectures. They should be compared by looking at how storage is presented to systems, how users access data and what the infrastructure needs to achieve.
Practical example: NAS, DAS or SAN?
For shared office files, NAS is often the natural architecture to evaluate first.
Scenario: A 25-user office needs shared departmental files, central backup storage and controlled user access.
A NAS is a natural candidate because it provides file services over the existing network. A directly attached enclosure would tie the storage more closely to one host. A SAN would make more sense where servers require shared block storage, for example in a more complex virtualisation environment.
Decision: For this example, start by evaluating NAS capacity, drive type, network speed, snapshots and backup replication. Do not deploy SAN architecture merely because it sounds more enterprise.
Common mistakes and selection checklist
Common mistakes
- Choosing NAS, DAS or SAN because one architecture sounds more enterprise rather than because it fits the workload.
- Sizing storage only by terabytes and ignoring IOPS, throughput, network speed, snapshots and backup.
- Using one storage system as both primary data and the only backup copy.
What happens if you get it wrong?
Users can experience slow file access or applications can be constrained by the wrong storage path. More importantly, a storage failure or data-loss event can affect both production data and the supposed recovery copy.
Selection checklist
- Decide whether applications need file storage, block storage or storage attached to one host.
- Estimate current usable capacity and realistic growth.
- Identify performance, network and concurrency requirements.
- Check drive type, RAID options, snapshots and expansion.
- Design backup and off-system recovery independently.
A resilient array keeps services available during some drive failures. Separate backups provide recovery from deletion, corruption, malware and site loss.
NAS
Network-attached storage provides storage over a network. It is commonly used where multiple users or systems need shared access to files and other data.
SAN
A storage area network is a dedicated storage networking architecture in which storage is presented to servers. It is generally considered in environments where centralised storage and server connectivity are important design considerations.
DAS
Direct-attached storage is connected directly to a server or host rather than being presented through a general network storage architecture.
| Approach | Basic connection model | Typical consideration |
|---|---|---|
| NAS | Storage accessed over a network | Shared files and network-accessible data |
| SAN | Storage presented through a storage network | Centralised storage for server environments |
| DAS | Storage directly attached to a host | Storage associated directly with a particular system |
There is no universal winner
The correct architecture depends on the applications, number of systems, performance requirements, capacity, availability requirements and budget. The storage architecture should follow those requirements.
Do not forget backup
NAS, SAN and DAS describe how storage is provided. None of them, by themselves, defines a complete backup strategy.
- What data needs to be stored?
- Who or what needs access to it?
- How many systems need storage access?
- What performance is required?
- What availability is required?
- How will the data be backed up?
Confirm the exact product specification, supported configuration and compatibility before ordering. Platform generation, firmware, licences and optional components can change what a product supports.