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.
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.