Computer network
A computer network is a collection of Computer and devices connected by communications channels that facilitates communications among users and allows users to save time, money and share resources with other users.
Networks are often classified as Local Area Network (LAN), Wide Area Network(WAN),Metropolitan Area Network (MAN), Virtual Private Network (VPN), Campus Area Network(CAN), Storage Area Network (SAN), and others, depending on their scale, scope and purpose.
Local area network
A Local Area Network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings.
Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist.
Specialized operating system software may be used to configure a local area network. For example, most flavors of Microsoft Windows provide a software package called Internet Connection Sharing (ICS) that supports controlled access to LAN resources
Wide area network
A Wide Area Network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies.
WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by ISPs, provide connections from an organization's LAN to the Internet. WANs are often built using Leased Lines At each end of the leased line a router connects to the LAN on one side and a hub within the WAN on the other.
Storage area network
A storage area network (SAN) is an architecture to attach remote Computer Data Storage devices (such as disk arrays, tape libraries and optical jukeboxes to servers so the devices appear as locally attached to the Operating System. A SAN typically has its own network of storage devices that are generally not accessible through the regular network by regular devices. The cost and complexity of SANs dropped in the late 2000's, resulting in much wider adoption across both enterprise and small to medium sized business environments.
Historically, data centers first created "islands" of SCSI disk arrays as Direct Attached Storage (DAS), each dedicated to an application, and visible as a number of "virtual hard drives" (i.e. LUNs). Essentially, a SAN consolidates such storage islands together using a high-speed network.
Operating systems maintain their own file system on them on dedicated, non-shared LUNS, as though they were local to themselves. If multiple systems were simply to attempt to share a LUN, these would interfere with each other and quickly corrupt the data. Any planned sharing of data on different computers within a LUN requires advanced solutions, such as SAN file systems or clustered computing
Despite such issues, SANs help to increase storage capacity utilization, since multiple servers consolidate their private storage space onto the disk arrays.
Common uses of a SAN include provision of transactionally accessed data that require high-speed block-level access to the hard drives such as email servers, databases, and high usage file servers.
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