June 15, 2009, 3:14 AM — A network-attached storage (NAS) device is a server that is dedicated for file sharing. NAS does not provide any of the activities that a server in a server-centric system typically does such as e-mail, authentication or file management.
NAS allows more hard disk storage space to be added to a network that already utilizes servers without shutting them down for maintenance and upgrades. With a NAS device, storage is not an integral part of the server. Instead, in this storage-centric design, the server still handles all of the processing of data but a NAS device delivers the data to the user. A NAS device does not need to be located within the server but can exist anywhere in a LAN and can be made up of multiple networked NAS devices.
NAS provides both storage and file system. This is often contrasted with SAN (Storage Area Network), which provides only block-based storage and leaves file system concerns on the "client" side. Most of the widely used SAN protocols are SCSI, Fibre Channel, iSCSI, ATA over Ethernet (AoE), or HyperSCSI.
Determine the need for NAS: Before choosing 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 well suited with 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.
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.
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.
Product operation: Storage 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.
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. 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.
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 is vital 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.
Uses:
NAS is useful for more than just general centralized storage provided to client computers in environments with large amounts of data. NAS can enable simpler and lower cost systems such as load-balancing and fault-tolerant email and web server systems by providing storage services. The potential emerging market for NAS is the consumer market where there is a large amount of multi-media data. Such consumer market appliances are now commonly available.
Unlike their rack mounted counterparts, they are generally packaged in smaller form factors. The price of NAS appliances has plummeted in recent years, offering flexible network-based storage to the home consumer market for little more than the cost of a regular USB or FireWire external hard disk. Many of these home consumer devices are built around ARM, PowerPC or MIPS processors running an embedded Linux operating system
