12-12-2017, 09:12 AM
A storage area network (SAN) is a network that provides access to consolidated block level data storage. SANs are mainly used to improve storage devices, such as disk arrays, tape libraries and optical jukeboxes, accessible to servers so that devices are displayed to the operating system as locally connected devices. A SAN generally 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 declined in the early 2000s to levels that allow for broader adoption in business environments and small- and medium-scale commercial environments. A SAN does not provide file abstraction, only block-level operations. However, file systems built on SAN provide file-level access and are known as shared disk file systems.
Historically data centers first created "islands" of SCSI disk arrays as Direct Attached Storage (DAS), each dedicated to an application, often visible as a number of "virtual hard drives" addressed as Logical Unit Numbers. (MON). Essentially, a SAN consolidates such storage islands together through a high-speed network. Operating systems maintain their own file systems on their own dedicated and non-shared LUNs, as if they were local to themselves. If several systems were simply to try to share a LUN, these would interfere with each other and quickly corrupt the data. Any planned exchange of data on different computers within a LUN requires software, such as SAN file systems or clustered computing. Despite these problems, SANs help to increase the use of storage capacity, since several servers consolidate their private storage space in the disk arrays. Common uses of a SAN include the provision of transactionally accessed data that requires high-speed block-level access to hard disks, such as email servers, databases, and high-use file servers.