DAS vs NAS vs SAN: Key Differences Explained

This article compares Direct Access Storage (DAS), Network Attached Storage (NAS), and Storage Area Network (SAN) solutions. We’ll explore their architectures, advantages, and disadvantages to help you choose the right storage for your needs.

DAS - Direct Access Storage

Fig-1: DAS Network

• The figure-1 depicts DAS network. It is a block level storage system.
• It is building block for both NAS and SAN.
• As shown, DAS system is directly attached to server or workstation. It doesn’t need any intermediary storage.
• DAS offers the highest performance of the three options, as it interfaces directly with the storage.
• DAS service is limited to the particular host it’s connected to. Other hosts can’t use it until it’s made available to them via SAN or NAS.
• A DAS controller unit can allow up to four servers to access the same logical storage device.
• Protocols like FC (Fibre Channel), SATA, SCSI, PATA or SATA are used for communication between computers/servers and DAS storage systems.

Fig-2: DAS architecture

• The figure-2 depicts DAS software architecture components.
• The storage disk system is managed directly by the client’s OS (Operating System).
• Software applications access data through the file I/O system available in the OS.
• File-level I/O initiated by a client application is mapped to block-level I/O transfers, which happen over the interface between the client PC and the disk system.

Advantages of DAS (Direct Access Storage)

• Dedicated storage resource.
• Inexpensive solution.
• Simple to configure.

Disadvantages of DAS

• The major disadvantage is the inability of DAS to efficiently share data or unused resources with other servers. NAS and SAN address this, but potentially at the risk of security and higher initial cost.
• De-centralized Storage
• No Storage Consolidation
• No High Availability
• Low Performance

NAS - Network Attached Storage

Fig-3: NAS Architecture

• The figure-3 depicts NAS architecture. It’s a file-level computer storage device designed specifically for serving files.
• As shown, NAS uses shared storage on a Local Area Network (LAN).
• It employs standard network and file sharing protocols like FTP, SMB, and CIFS.
• Communication with a NAS device happens at the file level.
• NAS is like a home or corporate network that allows access to data from anywhere with a great amount of privacy. Moreover, with NAS, you can often avoid regular monthly subscriptions.

Advantages of NAS (Network Attached Storage)

• Suitable for low-volume access to a large amount of storage by many users.
• Heterogeneous environment support.
• Centralized Storage

Disadvantages of NAS

• Lower Performance compared to DAS.
• Limited scalability.
• Network Congestion during backups & restores.
• Ethernet Limitations

SAN - Storage Area Network

Fig-4: SAN Architecture

• The figure-4 depicts SAN architecture. It’s an architecture designed to attach remote storage in a way that makes it appear as though it’s locally attached. Unlike NAS, which operates on files, SAN operates on blocks.
• LUN (Logical Unit Number) defines a virtual partition in a SAN. It’s mainly used for efficient storage utilization and for moving and reallocating storage.
• For example, if there are three servers (e.g., S1, S2, and S3) with a capacity of 500 GB each, connected with SAN, and S1 and S2 have only 100 GB used while S3 is used fully and has almost no space left. With SAN architecture, the unused space of Servers S1 and S2 can be allocated to Server S3. This allows efficient usage of storage spaces throughout the network. This can avoid the need to buy extra storage devices.
• Fibre Channel is a common SAN architecture, although other network standards can be used.
• SAN utilizes existing ethernet networks to connect to servers.
• It can be connected with any IP networks as well as Fibre Channels.

Advantages of SAN (Storage Area Network)

• The solution for terabytes of storage and multiple simultaneous accesses to files (e.g., streaming audio/video).
• Heterogeneous environment support.
• Centralized Storage Management.
• High Degree of Fault Tolerance.
• Best and superior performance.
• Storage Consolidation.
• Fast and efficient backups and restores.
• Dynamic Scalability.

Disadvantages of SAN

• Expensive solution for small setups.

Comparison: DAS vs NAS vs SAN

Let’s summarize the key differences in a table: