A storage area network (SAN) is a network that provides access to consolidated lock level data storage. SANs are primarily used to enhance storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear on the operating system as locally connected devices. Typically, a SAN has its own network of storage devices that are generally not accessible through the local area network (LAN) by other devices. The cost and complexity of SANs fell in the early 2000s to levels that allowed for greater adoption in both enterprise environments and small and medium business environments.
A SAN does not provide file abstraction, only block-level operations. However, file systems built on top of SANs provide file-level access and are known as shared disk file systems. Historically, data centers first created "islands" of SCSI disk arrays as direct storage (DAS), each dedicated to an application, often visible as a number of "virtual hard disks". Essentially, a SAN consolidates such storage islands together using a high-speed network.
Operating systems maintain their own file systems on their own dedicated and unshared LUNs, as if they were local to themselves. If multiple systems simply attempted to share a LUN, they would interfere with each other and corrupt data quickly. Any planned exchange of data on different computers within a LUN requires software, such as SAN file systems or clustered computing.
Despite these issues, SANs help increase storage utilization as multiple servers consolidate their private storage space into disk arrays. Common uses of a SAN include the provision of transactional access data that requires block-level high-speed access to hard disk drives such as high-use e-mail servers, databases, and file servers.
