DAS vs NAS vs SAN | difference between DAS,NAS,SAN

This page compares DAS(Direct Access Storage) vs NAS(Network Attached Storage) vs SAN(Storage Area Network) and mentions difference between DAS(Direct Access Storage),NAS(Network Attached Storage) and SAN(Storage Area Network). The architectures, advantages and disadvantages of DAS, NAS and SAN are also covered.

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 does not require any storage in between them.
• DAS offers highest performance among the three as it interfaces directly with storage.
• DAS service is limited to particular host and it can not be used by other hosts until it is made available to them using either SAN or NAS.
• DAS controller unit allows upto maximum of 4 servers to have access with same logic storage device.
• Protocols such as FC (Fiber Channel), SATA, SCSI, PATA or SATA are used between computers/servers and DAS storage systems.

Fig-2: DAS architecture

The figure-2 depicts DAS software architecture components. As shown storage disk system is managed directly by client OS (Operating System). Software applications can access data through file I/O system calles available in OS. The file level I/O initiated by client application is mapped into block level I/O transfers which happens over interface between client PC and disk system.

Advantages of DAS (Direct Access Storage)

Following are the advantages of DAS:
• Storage resource is dedicated.
• DAS solution is inexpensive.
• Simple to Configure

Disadvantages of DAS

Following are the disadvantages of DAS:
• The major disadvantage is inability of DAS to share data or unused resources with other servers efficiently. This is addressed by NAS ans SAN but 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 is a file level computer storage designed specifically for serving files.
• As shown NAS uses shared storage on Local Area Network.
• It uses standard network and file sharing protocols such as FTP, SMB and CIFS.
• The communication with NAS device happens at file level.
• NAS is like a home or corporate network which allows access of data from anywhere with great amount of privacy. Moreover with NAS one can avoid regular monthly subscriptions.

Advantages of NAS (Network Attached Storage)

Following are the advantages of NAS:
• It is used for low volume access to a large amount of storage by many users.
• Heterogeneous environment
• Centralized Storage

Disadvantages of NAS

Following are the disadvantages of NAS:
• Low Performance
• Limited scalability
• Network Congestion during backups & Restore
• Ethernet Limitations

SAN-Storage Area Network

Fig-4: SAN Architecture

The figure-4 depicts SAN architecture. It is a architecture to attach remote storage to make it appear as though it is locally attached. Unlike NAS which operates on files, SAN operates on blocks. LUN (Logical Unit Number) defines virtual partition in SAN.

It is 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) having capacity of 500 Gbytes each. These are connected with SAN and let us assume that S1 and S2 has only 100 GB used and rest are unused storage while S3 is used fully and has almost no space left. With SAN architecture, unused space of Servers S1 and S2 can be allocated to be used on Server S3. Hence SAN makes efficient usage of storage spaces throughout the network. Due to this feature, one can avoid extra expenditure to buy the extra storage devices in SAN.

Fiber channel is defacto SAN architecture, although other network standards can be used. SAN utilizes existing ethernet networks to connect SAN with servers. It can be connected with any IP networks as well as fiber channels.

Advantages of SAN (Storage Area Network)

Following are the advantages of SAN:
• It is solution for terabytes of storage and multiple simultaneous access to files e.g. streaming audio/video.
• Heterogeneous environment
• 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

Following are the disadvantages of SAN:
• Expensive solution for small setups

Comparison or difference between DAS, NAS and SAN

Let us summarize comparison factors as difference between DAS storage, NAS storage and SAN storage types in the tabular form.

feature	DAS	NAS	SAN
Full Name	Direct Access Storage	Network Attached Storage	Storage Area Network
Storage type	Sectors	Shared files	Blocks
Data Transmission	IDE/SCSI	TCP/IP, Ethernet	Fiber Channel, IP
Access Mode	Clients or servers	Clients or servers	Servers
Capacity in Bytes	10⁹	10⁹ to 10¹²	> 10¹²
Complexity	Easy	Moderate	Difficult
Management cost (per GB)	High	Moderate	Low

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