NAS Definitions and Product Classes

Posted on April 01, 1998

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NAS Definitions and Product Classes

Farid Neema

Peripheral Concepts Inc.

Network-attached storage (NAS) connects directly to the network and is optimized for better overall data accessibility. The system has a processor and its own operating system to allow network connectivity. The ability of NAS servers to connect anywhere on a LAN allows network performance to be balanced by placing storage close to the users who need to have data readily accessible.

A NAS architecture is particularly effective when the network is segmented by bridges, routers, or switches. With NAS, additional storage can be integrated at any location without changing the overall storage strategy; the exact amount of storage needed is plugged in for modular, incremental growth. And host platform independence and direct network connectivity allow corporations to retain their prior investments in storage devices as their environment changes.

NAS essentially replaces host servers with dedicated computers for network protocol processing and file serving. File services support data at the file level and offer greater flexibility in storage and data management, as well as higher performance in accessing files.

Implementations of network-attached storage range from very simple attachment of a limited amount of storage--as little as a disk drive or a CD-ROM--to a full-function "intelligent" system dedicated to storage. The former is sometimes referred to as network-ready storage (NRS); the latter, as a network-attached storage server (NASS).

Network-ready storage implementations differ according to the characteristics emphasized by a vendor and to the breadth of storage technologies and devices they support. Many implementations limit server functionality to satisfy the plug-and-play concept. However, this approach may not provide the additional reliability of higher-end implementations.

Within the NASS market, there are three product classes, although no hard boundaries exist among the classes.

- In Peripheral Concepts` terminology, a class-1 storage server is resistant to the most common failures (e.g., disk drive, power supply, and cooling system), but it is still vulnerable to less-common component failures and most often must be turned off for planned maintenance. Its connectivity is limited to one network protocol (e.g., Ethernet) and one file system.

- A class-2 storage server has no single point of failure, and field-replaceable units can be swapped while the system operates. It incorporates some performance features, such as faster write for RAID configurations, complex caching algorithms, and dedicated data paths. The system can be scaled many ways, allowing easy growth in performance, resiliency, and connectivity. An integrated backup solution is usually offered as an option, and administration of all network-connected storage can be performed from one central location.

- Features contained in a class-3 storage server include connectivity to several network topologies and file systems, which may include proprietary systems and mainframes. Performance is improved through automatic load and path balancing, and high-speed transfers between storage domains assigned to different file or application servers. Accessibility is enhanced by features that ensure disaster protection. Failing components are self-diagnosed and are reported to a remote service site to be corrected or replaced before they become inoperative.

Class-3 storage capacity can be scaled to over one terabyte within a single enclosure.

Farid Neema is president of Peripheral Concepts Inc., a storage market research and consulting firm, in Santa Barbara, CA.


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