516 IBM Midrange System Storage Hardware Guide
iSCSI technology
iSCSI is a protocol that transmits SCSI commands and data over a standard Transmission
Control Protocol/Internet Protocol (TCP/IP) based network. The advantage to using a
TCP/IP-based network instead of an Fibre Channel based infrastructure is largely based on
the cost associated with implementation and support of a Fibre Channel (FC) SAN. In many
organizations, a TCP/IP based network already exists and is already being utilized for IP
traffic over Local Area Network (LAN) and Wide Area Network (WAN). More recently, the
TCP/IP network has also been used for voice traffic with the development of Voice over IP
(VoIP). So for some organizations, further use of this existing resource with iSCSI makes
sound economic sense.
The iSCSI protocol can be used to transmit data from the connected server to the storage
subsystem and vice versa. Generically, the servers are called “initiators”, and the storage
subsystem iSCSI ports, such as those available on the IBM DS5000 storage subsystems, are
known as “targets”. The targets will listen for connection requests using TCP port 3260 (you
can use another port if necessary). You may create other Ethernet ports to handle
subsequent communications after a connection between initiator and target is established. An
active iSCSI connection is called a
session, and a session is required for actual data transfer
to occur.
Figure B-1 iSCSI communication components
For the initiator to communicate with the target, you must assign a unique name to both, so
that this communication layer can be established. Two types of naming conventions are
associated with iSCSI: the IQN, or iSCSI qualified name, and the EUI, or the IEEE EUI-64
identifier.
Support is provided for IQN names on the IBM DS5000 series of storage subsystems.
iSCSI Qualified Name (IQN)
Four major sections comprise an IQN:
Type
Date
Naming authority
Unique string
Target
Initiator
iSCSI Device
Discovery
IP
SCSI (Block I/O) Protocol
Application Server
Client Desktop
Initiator
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