iSCSI, TARGET AND LUN

What is iSCSI?

iSCSI - Internet SCSI (Small Computer System Interface) 

iSCSI is an IP-based storage networking standard for linking data storage facilities, developed by the Internet Engineering Task Force (IETF). By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances.

iSCSI SANs use Ethernet connections between computer systems, or host servers, and high performance storage subsystems. The SAN components include iSCSI host bus adapters (HBAs) or Network Interface Cards (NICs) in the host servers, switches and routers that transport the storage traffic, cables, storage processors (SPs), and storage disk systems.

What is TARGET?

Targets are created in order to manage the connections between an iSCSI device and the servers that need to access it. A target defines the portals (IP addresses) that can be used to connect to the iSCSI device, as well as the security settings (if any) that the iSCSI device requires in order to authenticate the servers that are requesting access to its resources.

What is LUN?

Logical unit numbers (LUNs) created on an iSCSI disk storage subsystem are not directly assigned to a server. For iSCSI, LUNs are assigned to logical entities called targets.

Servers that require access to a LUN have to connect to the target to which the LUN is assigned. To connect to a target, a server in the storage area network (SAN) uses an iSCSI initiator. An iSCSI initiator is a logical entity that enables the server to communicate with the target. The iSCSI initiator first logs on to the target. The target must grant access before the server can start reading and writing to all LUNs that are assigned to that target.