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How does network-attached storage work?

By Deni Connor

Network-attached storage (NAS) devices connect to a Gigabit Ethernet network and give users access to files stored on an appliance.

NAS appliances evolved out of traditional file-server environments and have both storage capacity and a file system. Like file servers, NAS devices are equipped with less expensive, slower Serial Advanced Technology Attachment or faster, more expensive Fibre Channel drives.

NAS devices come with three varieties of file systems -- those that support Microsoft's Common Internet File System, those that support the Unix/Linux Network File System and those that work with both protocols.

NAS systems range in size from 500GB at the low end to large systems offering as much as two petabytes of storage capacity. Each NAS system has its own operating system, either Microsoft Windows or a proprietary OS. Unlike storage-area network (SAN) arrays, the NAS appliance does not rely on a server to provide its access to users. A NAS system is much like a server, containing its own CPU, motherboard and RAM.

Like SAN arrays, NAS appliances have a number of high-availability, replication and clustering capabilities, depending on their size and price.

NAS got its start in early file-sharing environments, such as Novell's NetWare, which used the NetWare Core Protocol. In 1984, Sun developed the Network File System. In 1992, a group of engineers from early NAS vendor Auspex founded Network Appliance, making it the first company to implement NAS as an appliance. Today, some companies, including Isilon and PolyServe (acquired by HP), are clustering NAS devices under a single global file system.

Earlier this decade, Microsoft began offering storage products, and the first were NAS appliances using Windows Server 2003. These devices are marketed and developed by companies that include Dell, HP, Iomega and EMC. Windows Storage Server 2003 R2 devices include advanced availability features, such as point-in-time data copies, replication and server clustering.

NAS gateways have also been developed. In a NAS gateway, a NAS front-end attaches to the SAN and provides file-level access to the SAN's block-level storage. ONStor's Bobcat gateway is an example. NAS vendors have also started to incorporate block-level access into their appliances and call them unified storage. Among the vendors that provide such storage are Network Appliance, Pillar Data and BlueArc.

This story, "Guide to Network Attached Storage" was originally published by Network World.

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