"During the communication between a host and storage, a
host generally acts as a SCSI initiator. In computer storage, the
SCSI initiator is the endpoint that initiates a SCSI session,
meaning it sends a SCSI command. The storage often acts as a SCSI
target which receives and processes SCSI commands. The SCSI target
waits for the initiator's commands and then provides required
input/output data transfers.
"The target usually provides the initiators one or more logical
unit numbers (LUN). In computer storage, a LUN is simply the number
assigned to a logical unit. A logical unit is a SCSI protocol
entity, the only one which may be addressed by the actual I/O
operations. Each SCSI target provides one or more logical units; it
does not perform I/O as itself, but on behalf of a specific logical
"In a storage area, a LUN often represents a SCSI disk on which
a host can perform a read and write operation. Figure 1 shows how
the SCSI client/server model works."