What is the difference between san and nas

Both network-attached storage (NAS) and storage area network (SAN) were developed to solve the problem of making stored data available to a lot of users at once. Each of them provides dedicated storage for a group of users, but they couldn’t be more different in their approach to achieving their mission.

A NAS is a single storage device that serves files over Ethernet and is relatively inexpensive and easy to set up, while a SAN is a tightly coupled network of multiple devices that work with block-based data and is more expensive and complex to set up and manage. From a user perspective, the biggest difference between NAS and SAN is that NAS devices look like volumes on a file server and use protocols like NFS and SMB/CIFS, while SAN-connected disks appear to the user as local drives.

We provide an overview of the differences between NAS and SAN below. We’ll also briefly cover solutions that combine NAS and SAN and offer many of the advanced benefits of SAN without its high cost.

Basic Definitions — What is NAS?

A NAS is a computer connected to a network that provides file-based data storage services to other devices on the network. The primary strength of NAS is how simple it is to set up and deploy. NAS volumes appear to the user as network mounted volume. The files to be served are typically contained on one or more storage drives, often arranged into logical, redundant storage containers or RAID. The device itself is a network node, much like computers and other TCP/IP devices, all of which maintain their own IP address and can effectively communicate with other networked devices. Although a NAS is usually not designed to be a general-purpose server, NAS vendors and third parties are increasingly offering other software to provide server-like functionality on a NAS.

NAS devices offer an easy way for multiple users in diverse locations to access data, which is valuable when uses are collaborating on projects or sharing information. NAS provides good access controls and security to support collaboration, while also enabling someone who is not an IT professional to administer and manage access to the data. It also offers good fundamental data security through the use of redundant data structures — often RAID — and automatic backup services to local devices and to the cloud.

Benefits of NAS

A NAS is frequently the next step up for a home office or small business that is using DAS (direct attached storage). The move up to NAS results from the desire to share files locally and remotely, having files available 24/7, data redundancy, the ability to replace and upgrade hard drives in the system, and and the availability of other services such as automatic backup.

Summary of NAS Benefits

• Relatively inexpensive
• 24/7 and remote data availability
• Good expandability
• Redundant storage architecture
• Automatic backups to other devices and cloud
• Flexibility

Limitations of NAS

The weaknesses of a NAS are related to scale and performance. As more users need access, the server might not be able to keep up and could require the addition of more server horsepower. The other weakness is related to the nature of Ethernet itself. By design, Ethernet transfers data from one place to another via packets, dividing the source into a number of segments and sending them along to their destination. Any of those packets could be delayed, or sent out of order, and might not be available to the user until all of the packets arrive and are put back in order.

Any latency (slow or retried connections) is usually not noticed by users for small files, but can be a major problem in demanding environments such as video production, where files are extremely large and latency of more than a few milliseconds can disrupt production steps such as rendering.

Basic Definitions — What is SAN?

A SAN is a way to provide users shared access to consolidated, block level data storage, even allowing multiple clients to access files at the same time with very high performance. A SAN enhances the accessibility of storage devices such as disk arrays and tape libraries by making them appear to users as if they were external hard drives on their local system. By providing a separate storage-based network for block data access over high-speed Fibre Channel, and avoiding the limitations of TCP/IP protocols and local area network congestion, a SAN provides the highest access speed available for media and mission critical stored data.

Benefits of SAN

Because it’s considerably more complex and expensive than NAS, SAN is typically used by large corporations and requires administration by an IT staff. For some applications, such as video editing, it’s especially desirable due to its high speed and low latency. Video editing requires fair and prioritized bandwidth usage across the network, which is an advantage of SAN.

A primary strength of a SAN is that all of the file access negotiation happens over Ethernet while the files are served via extremely high speed Fibre Channel, which translates to very snappy performance on the client workstations, even for very large files. For this reason SAN is widely used today in collaborative video editing environments.

Summary of SAN Benefits

• Extremely fast data access
• Dedicated network for storage relieves stress on LAN
• Highly expandable
• OS level (block level) access to files
• High quality-of-service for demanding applications such as video editing

Limitations of SAN

The challenge of SAN can be summed up in its cost and administration requirements — having to dedicate and maintain both a separate Ethernet network for metadata file requests and implement a Fibre Channel network can be a considerable investment. That being said, SANs are really the only way to provide very fast data access for a large number of users that also can scale to supporting hundreds of users at the same time.

NAS/SAN Convergence

The benefits of SAN are motivating some vendors to offer SAN-like products at lower cost chiefly by avoiding the high expense of Fibre Channel networking. This has resulted in a partial convergence of NAS and SAN approaches to network storage at a lower cost than purely SAN.

One example is Fibre Channel over Ethernet (FCoE), which supports block level transfers over standard LAN at speeds of 10GB/sec+. For smaller deployments, iSCSI is even less expensive, allowing SCSI commands to be sent inside of IP packets on a LAN. Both of these approaches avoid expensive Fibre Channel completely, resulting in slower, but less expensive ways to get the block level access and other benefits of a SAN.

Are You Using NAS, SAN, or Both?

If you are using NAS or SAN, we’d love to hear from you about what you’re using and how you’re using them. Also, please feel free to suggest other topics for this series.

— — Virbhadrasinh Gohil