Network Attached Storage (NAS)

Network-Attached Storage (NAS or "Network File Server") consists of fast disk (staging) storage and optionally, a large secondary (tape) storage. Network file servers can be attached to one network or to multiple networks and access to them is possible via one or more of the standard network protocols. In some cases, a proprietary protocol may also be used.

A file server is used tp provide a shared storage resource for network users. Users have the same type of access to their files as if they were stored locally - the only penalty is slower performance because of the various network overheads. When this is unacceptable, files can be fetched rapidly from the file server, stored locally, used, and then returned to the file server. In this case a protocol such as FTP is used to get files from and put them back into the file servers. Machines that have a large amount of disk storage can be connected to the file server via a fast link. In the past, connections such as UltraNet, HIPPI etc. were used. Fibre Channel is now the most common method for high-speed connectivity.

The file server's staging storage is usually JBOD; in special cases, where high performance is essential, it can be implemented through parallel disk arrays or software disk striping. Secondary storage is usually implemented through some type of tape, for example, the STK 9840 tape, or other tape depending on performance requirements. At the start of the 1990s, Network file servers were the primary means of sharing large-scale storage between network users. Today, Fibre Channel and SANs are being used for high-speed connectivity between machines.

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