Storage Area Networks

A storage area network, or SAN, connects servers to shared block storage through a dedicated storage fabric or storage-capable network. Hosts issue storage commands as initiators. Storage systems receive them as targets and present logical units. The host then treats each permitted logical unit as a block device.

An application reaches a host file system or database, which issues block requests to a logical device. Multipath software combines approved paths. Each path leaves a host adapter or network interface, crosses one or more switches, reaches a target port, and accesses a logical unit on the storage system. Zoning controls fabric communication, while logical-unit masking controls which initiators can access a presented unit.

The SCSI model separates roles

An initiator starts storage commands. A target receives them. A logical unit is a storage address presented by the target, commonly identified by a LUN in the SCSI model. Stable initiator and target identifiers matter because adapter locations and network addresses can change. Presentation must be coordinated with host ownership.