While storage area networks (SAN) provide substantial performance and utilization benefits for a data center, not every organization can justify the cost and complexity involved. In many cases, storage can be added to the network using network attached storage (NAS) devices -- dedicated disk-based storage devices that attach to the user local area network (LAN) through an ordinary network connection. NAS devices can be expanded with additional disks, and new NAS appliances can be added as needed to facilitate significant amounts of network storage. Not all NAS devices include their own storage. NAS gateways basically provide NAS functionality to externally connected storage; most often through a Fibre Channel (FC) connection. Thus, a NAS gateway can connect to a storage array or SAN storage.
NAS management software tools will need to be selected to identify available storage, handle backup and restore tasks, support replication and tackle a variety of other data protection tasks. Most NAS devices include vendor-specific management tools, but there are some generic tools intended to provide heterogeneous NAS platform support. Aside from considering the obvious issues of pricing, management and support, here are some other important points to keep in mind during any NAS purchase.
Determine the underlying need for NAS. Before selecting a storage platform, consider the applications that will be using the storage -- storage should accommodate the applications, not vice versa. Some file-based application data, such as images and Word documents, are better suited to NAS platforms. Block-based applications, like databases, may achieve better performance through SAN storage. It is also possible to mix architectures using a NAS gateway to allow file-based access to SAN storage.
Consider storage needs over the long haul. NAS may be easy to implement and expand, but it can become difficult to manage as deployments proliferate. Before making a NAS investment, consider the changing patterns of storage allocation and use in your enterprise. For example, several terabytes (TB) of NAS might meet immediate needs, but adding several TB per year across numerous NAS devices might soon become impossible to administer. In those situations, an investment in SAN might be more appealing or opt for a large-capacity NAS up front to consolidate storage systems early on. Also, explore potential upgrade paths to learn how future updates will impact storage performance and total cost. For example, more expensive NAS platforms may be more cost-effective over time if they are easier and cheaper to upgrade.
Consider different modes of implementation. Generally speaking, there are three ways to implement NAS -- use a dedicated NAS system (appliance) with its own local storage; use a NAS head or gateway to access external storage on an array or SAN; or some combination of both approaches. Dedicated NAS appliances are often preferred when simplicity and ease of deployment is most important and little scalability is needed. NAS gateways provide access to considerably more potential storage, but can be more complex to manage due to the provisioning and security implications of SAN storage. Weigh the tradeoffs carefully before choosing an approach.
Consider product utilization and value. Industry experts note that NAS selection criteria should extend beyond getting the most storage for the minimum cost. The problem is that many NAS features have little tangible value other than differentiating vendors. In addition to the cost/capacity tradeoff, take an honest look at the features and functionality that you will actually use. For example, it may be worth spending a little more up front for key features that improve performance or ease management; as long as the real benefits outweigh the costs. Conversely, exotic features (e.g. remote snapshots) may look appealing on paper, but they're not worth the added price if you never intend to use them. Weigh the impact of related factors like reliability, ease-of-use, vendor support and interoperability.
Consider the management overhead. NAS appliances and gateways will need to be managed using software tools. Management overhead will typically increase as NAS storage expands and proliferates across multiple devices. Over time, NAS management overhead can become unwieldy -- working against the ease and simplicity that NAS is known for. Make sure that any NAS management tools support the NAS hardware deployed across your infrastructure. Try to avoid multiple tools if possible. NAS appliances with internal storage offer convenience, but NAS gateways are sometimes selected when heavy storage demands are expected "outside of the box." Difficult management can sometimes be eased by consolidating multiple NAS devices into a single NAS platform or shifting NAS storage to the SAN using a NAS gateway. Virtualization can also be applied to achieve a higher level of intelligence, ease management and improve utilization of the physical storage.
Evaluate the performance of any potential NAS device. LAN connectivity can be a potential bottleneck with NAS devices, and storage performance can suffer with heavy network traffic or storage I/O requests. It's important to test the performance of your applications running on a prospective NAS device. Ensure that the NAS device can meet the I/O and latency demands of the applications. When high performance and availability are needed, select a NAS system with multiple high-speed LAN ports that support aggregation and failover. It's also worth examining performance against scalability to ensure that the NAS product will continue to perform adequately as it scales up.
Define any new or different skill sets that are required. Although NAS devices offer a lot of similarities, there are also subtle, and sometimes not so subtle, differences between models and manufacturers. For example, some NAS boxes run common operating systems (OS), such as Windows, while others may utilize a manufacturer-specific OS. When studying the requirements of a prospective purchase, you should identify areas where IT staff may need additional or supplemental training to install, configure and support the NAS box. New skill sets often cost money, raising the total cost of ownership (TCO) of a prospective purchase. In many cases, lab testing prior to a purchase can familiarize staff with basic NAS operations, allowing them to ask more informed and pointed questions during manufacturer training sessions.
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