How much data storage do you need now?

This is the basic question you need to answer when adding NAS to your data storage environment. How much storage do you have now? Are you trying to replace all the data storage on your system with NAS storage, supplement what you have, or provide storage for a particular application? Answering these questions will give you a basic foundation for understanding your NAS needs.

How much storage will you need in 18 to 24 months?

From a one terabyte appliance to a gateway backed by a petabyte or more of storage, NAS comes in all sizes -- at a price. The trick is to estimate how much storage you'll need in the forseeable future and get a NAS system that can handle that much data growth.

It's easy to get into a pattern of meeting immediate storage needs by adding another NAS device. However, that can result in management headaches as you try to handle a bunch of separate devices. It can also lead to inefficient use of storage resources because your total NAS capacity is scattered among different devices.

It is better to estimate your storage growth and purchase a system which can be expanded to keep pace with that growth. Start by looking at your logs to see how fast your storage needs have grown over the last year or so. Project that out and add a cushion -- usually 20% -- to arrive at your estimated growth.

Most of the time, your best bet is to purchase a NAS device which is expandable, either by adding higher capacity disks to an appliance or by adding more disk arrays. All of the major NAS suppliers offer expandable NAS devices such as the SnapServer 620 from Overland Storage, which allows for up to 7 S50 JBOD Expansion Units.

Do you have the bandwidth on your LAN?

By its nature, NAS puts an additional load on your local area network (LAN) as files are shipped back and forth between the NAS device and the users. If your network is already near capacity, the performance of even the fastest NAS device will be disappointing.

How much bandwidth you need depends on the current load on the network and the load the NAS will add. The added load in turn depends on the way you will use NAS. Generally speaking, it is easier for NAS to handle many little to medium-sized files than a few large ones. Shipping big graphics files around with fast response times takes more network capacity than moving small- to medium-sized files over the network.

A good way to determine whether or not you have enough bandwidth is to look at your LAN's log files. Check to see how heavily loaded your existing LAN is and then extrapolate based on the size and number of files you'll be adding to the network load with NAS.

Except in small installations, you generally want at least a Gigabit Ethernet network or the equivalent. Similarly, if you use routers or gateways, keep the NAS device topologically close to the users.

How well will network-attached storage integrate with your data storage management?

Just about anything that calls itself data storage management software will support at least some NAS devices. However, few of these applications will support all NAS devices on the market. You need to make sure that your storage management software -- whether existing or newly purchased -- will support all your storage. At a minimum, your SMS should be able to discover NAS on the network, configure it and provide a reasonable level of security for all your users.

Also, checking compatibility involves working with both the NAS and software vendors to make sure the combination will do what you want it to do.

Is the NAS device clusterable?

Clustering involves attaching NAS devices so they can work together. This improves performance by spreading the workload over more than one set of processors in the NAS devices. Clustering also offers better expandability, load balancing and increases the bandwidth between the NAS devices and the network.

Not all NAS devices are clusterable, although most of the midrange and nearly all the high-end NAS devices are clusterable. If your expansion plans call for significant increase in NAS capacity, i.e., doubling NAS storage or more, clustering is worth investigating both for the added reliability of redundancy and improved day-to-day performance.

Does the NAS device do scheduled backups?

A NAS device is a critical part of your data storage architecture and should have the ability to do automatic data backups on a schedule. The devices with this capability can typically be backed up either to an external disk connected to the NAS device via a USB port, or over the network to another disk or disk array. This feature is found on most NAS devices except the very smallest. Typically the NAS comes with a utility that will allow you to set up the backup schedule and will also take care of doing the backups. You may also want to schedule your backups through your data storage management software.

Buying NAS storage isn't especially complicated. It is mostly a matter of thinking about what you need now and what you will need in the future. Generally how much data storage you are adding will determine how much time and effort you will want to put into choosing a NAS device.