A Conceptual Overview of iSCSI

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Figure 6. Representation of an iSCSI Multi-Connection Session
The individual connections of a session may go through a variety of network infrastructure
components (network switches, routers, hubs, etc.). iSCSI is agnostic to the network infrastructure
components. The connection endpoints are the IP address/TCP port number pairs that identify the
network portals.
7. Portal Groups
A LUN view is a subset of the total set of SCSI LUNs accessible behind an iSCSI target node. To
provide a SCSI I-T Nexus with a constant LUN view, each connection of an iSCSI session must
have access to exactly the same LUN view. If, for some reason, any connection in a multi-
connection session were to terminate, the remaining connections of that session would still have
access to all of the LUNs in the LUN view.
Network portals accessing an iSCSI node and having the same SCSI LUN view can be grouped
together to define an iSCSI portal group. The portal group is identified by a portal group tag
uniquely defined for the iSCSI node.
To access a SCSI LUN View behind an iSCSI target node, an iSCSI address must include the
following information:
• the iSCSI node name
• the network portal IP address
• the network portal TCP port number
• the iSCSI target portal group tag
For access to a LUN view through a portal group, there is a single iSCSI node name and a single
iSCSI target portal group tag. Multiple network portals (IP address and TCP port pairs) may be
defined for a portal group to provide multiple points of access for a network entity through an iSCSI
target node to a particular LUN view.
The portal group tag is not necessary in iSCSI initiator node addresses.
iSCSI Initiator
Session
iSCSI
Target
Session
Connections
Network Portals