What is SAN(storage Area Network)and when we do we have to use it?

A storage area network is a network which provides access to consolidated, block level data storage.

A storage area network is a network which provides access to consolidated, block level data storage.

O.K I am going to explain it as a story.

In older days, computers had local disks but then as staorage demand increased local disks became unsufficient and then cam the Direct attached Storage systems but as Information Technology progressed and Need for Storage became more demanding and attaching a DAS to each computer became a nightmare so the idea of SAN emerged where all the disks are in one storage system (if you can afford, you can have multiple storage systems), the storage system can be connected to various computers using Fiber Channel or iSCSI for connectivity then a storage analyst will allocate chunks of disks from the storage system for computers that will be visible on the computer as a local disk (Keep in mind that either zoning or iSCSI mapping will be required for connection between Storage system and computer.)

SAN is nothing but a high speed, high availablity and fault tolerent Fiber Channel based network, which connects to storage array and provides additional block storage space to servers.

SAN comes in to picture when an IT environment needs additional storage space on its servers with high data transfer speed, high availablity, fault tolerance which conventional direct attached storage cannot cater.

A Storage Area Network (SAN) is a high-speed network that provides multiple servers access to consolidated pools of shared, block-level storage.

Your qus. having two parts. First qus. Ans. SAN or storage area network is a dedicated network that provides access to consolidated, block level data storage. Just think why we are creating LAN, to sharing some common resources to others computers. Same way SAN is for sharing storages( it can data, tape, etc) using special switches called SAN switch which create logical connection between initiator (host/server) and target (storage devices). Now ans of second qus. Also told in answer of first qus. In addition to that when systems require share storage resources, high disk spaces, high performance in terms of high disk IOPS, low latency then, SAN comes on picture as a requirement. It's include additional cost.

A storage area network (SAN) is a dedicated network that provides access to consolidated, block 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 like locally attached devices to the operating system. A SAN typically 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 dropped in the early2000s to levels allowing wider adoption across both enterprise and small to medium sized business environments.

A SAN does not provide file abstraction, only block-level operations. However, file systems built on top of SANs do provide file-level access, and are known as SAN filesystems or shared disk file systems.

Storage Area Networks is high perfromance network infrastructure for provisioning data storage to systems. Most common types are ISCSI and FC. SAN is independant of filesystem and can be in heterogenous file system/OS environment. SAN is more secure in comparison to other data storage due to isolation from public/user network. Main components of SAN: High speed data network infrastructure including FC/UTP cables/ISCSI cables,HBA (FC or ISCI1G or10G), Fiberchannel switches/ISCSI/Network Switches and Data Storage with Storage Controllers etc.

 

According to the Storage Networking Industry Association dictionary (and who should know better?):

A storage area network (SAN) is any high-performance network whose primary purpose is to enable storage devices to communicate with computer systems and with each other.

http://www.snia.org/education/storage_networking_primer/san/what_san

 

SAN storage is a network of storage devices that can be accessed by multiple computers .We have to use it in clustering and HA Solutions .