NAS vs SAN: A Helpful Guide


When it comes to network-based storage, network-attached storage (NAS) and storage-area networks (SAN) are two popular choices that complement each other. The reality is that they are completely different products that serve different purposes, and often coexist together in the same environment. Which one you choose will largely depend on your organization's needs. Let's look at some of the differences between NAS and SAN products.

SAN or NAS?

The idea that a company is faced with a choice between a SAN and a NAS is not an accurate scenario.  NAS and SANs are different tools for different jobs, just as a saw and a screwdriver are different tools for different jobs.  A SAN is a primary storage device.  It is the proper tool when critical data must be readily available - take a bank for example.   The transactions that are taking place at the teller window must be recorded and immediately available for verification.  If a customer makes a deposit and then writes a check against that deposit, the data showing the funds are in the account must be available.  A SAN must also be secure.  Ideally a SAN will have no single point of failure. To minimize exposure to loss of data, do not assume that every SAN has no single point of failure, because Not all SANs on the market are free of single points of failure. Check with your vendor to be sure, and do not be afraid to ask specific questions.  Backplane and I/O are frequent single points of failure found on SANs from some manufacturers.

Simplicity vs Speed

One of the main differences between NAS and SAN is simplicity.

A NAS is designed to be plugged directly into your existing network or LAN (or a separate VLAN or domain if it’s used for disaster recovery). Because its networking is based on TCP/IP, a NAS integrates into your network as any other device would, making it readily accessible to the other computers, tablets and devices accessing the LAN.  A NAS can be thought of as a massive thumb drive.

In contrast, the SAN utilizes iSCSI, Infiniband, or Fibre Channel to create its own network that is accessed by a virtualized server or servers in a virtual computing environment, rather than individual clients. The advantage of this approach is raw speed, since the SAN's network is segregated from the rest of the LAN and uses its own protocol.

Another factor affecting simplicity is the way each system deals with data. Because NAS traces its roots back to Microsoft file sharing, as well as Novell's NetWare, NAS automatically supports a number of modern networking protocols and file systems. What's more, most NAS setups also include administrative software to help manage file serving, automatic backups and other functions a NAS is commonly used for. A SAN, on the other hand, addresses data by blocks, rather than filenames or types, and is designed to offer a common pool of storage to a server or servers. While this certainly provides more raw potential, it also requires more knowledge and expertise to set up and manage.

When it comes to simplicity, a NAS system offers clear advantages, while a SAN wins for raw speed. This is an important difference between NAS and SAN.

Expansion

Both NAS and SAN devices are easily expandable with JBODs.

With a NAS setup, each NAS is a self-contained entity. It's often possible to expand the storage of a NAS, taking its capacity from terabytes to petabytes. Depending on the operating system, networking devices can be pooled, and the NAS devices can grow into a farm or cluster if required.

A SAN can similarly be expanded with JBODs, but each SAN server (since it’s comprised of two servers working in synchronized lock-step) must be expanded identically.  Since a SAN is duplicating data from primary to secondary, synching the SAN can be an issue as well.  A 24-48TB SAN can synch up with its partner in days.  A PB SAN could take weeks or months depending on the load.  While SANs are in synch mode, the critical data is exposed, and disaster recover from the synching device is non-existent.

In either case, the volume cannot increase without a re-formatting of the drives.  It is better to just add “new” volumes with the JBODs

Cost

Because of its much simpler design, NAS appliances are often far less expensive than SANs, in terms of hardware and management.

Convergence

As with many things in technology, as each solution continues to develop there is an increasing amount of overlap between the two options. Ethernet and TCP/IP networking continues to evolve and eat away at the speed advantage SANs currently hold. Meanwhile, improvements in file management and administrative software continue to lower the barrier to entry of SANs. 

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