HP-UX iSCSI Software Initiator Support Guide (Edition 7)

1 iSCSI Overview
This chapter contains information on:
• “iSCSI Protocol Overview” (page 5)
• “The iSCSI PDU” (page 6)
• “iSCSI Layering” (page 6)
• “iSCSI Session and TCP Connections” (page 7)
• “iSCSI Login” (page 8)
• “iSCSI Concepts: Network Entities, Portals, and Nodes” (page 9)
1.1 iSCSI Protocol Overview
NOTE: This chapter provides a brief, high level, overview of the iSCSI Protocol as defined by
RFC 3720. For comprehensive information on the iSCSI Protocol specification, consult RFC 3720
at: http://www.ietf.org/rfc/rfc3720.txt
Figure 1 iSCSI: A Transport Protocol Alternative that Operates Over TCP/IP
SCSI (Small Computer Systems Interface) is a widely implemented family of protocols used for
communication with I/O devices, particularly storage devices.
SCSI is a client-server architecture. Clients of a SCSI interface are called “initiators”. Initiators issue
SCSI “commands” to request services from “targets”. Targets are typically components, or logical
units, on a server.
A “SCSI transport” maps the client-server SCSI protocol to a specific interconnect. Initiators are
one endpoint of a SCSI transport and targets are the other endpoint. The SCSI protocol has been
mapped over various transports, including Parallel SCSI and Fibre Channel.
iSCSI is a transport protocol for SCSI, operating at the same level as Parallel SCSI and Fibre
Channel.
iSCSI is a storage transport protocol developed by the Internet Engineering Task Force (IETF) for
transporting SCSI packets over TCP/IP.
iSCSI provides an interoperable solution that takes advantage of existing Internet infrastructure
and Internet management facilities.
iSCSI does not have the distance limitations associated with the Fibre Channel storage transport.
The iSCSI protocol enables the transport of Block I/O over IP Networks. It operates on top of TCP
by encapsulating SCSI commands in a TCP/IP stream.
1.1 iSCSI Protocol Overview 5