What is SCSI-iSCSI Layer, Device and Port

Here is a listing of technical definitions for SCSI-iSCSI Layer, Device and Port.

iSCSI Layer: This layer builds/receives iSCSI PDUs and relays/receives them to/from one or more TCP connections that form an initiator-target “session”.

iSCSI Device: A SCSI Device using an iSCSI service delivery subsystem. Service Delivery Subsystem is defined by SCSI Architecture Manual as a transport mechanism for SCSI commands and responses.

SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor Blocks) and relays/receives them with the remaining command execute [SAM2] parameters to/from the iSCSI Layer.

SCSI Device: This is the SAM2 term for an entity that contains one or more SCSI ports that are connected to a service delivery subsystem and supports a SCSI application protocol. For example, a SCSI Initiator Device contains one or more SCSI Initiator Ports and zero or more application clients. A Target Device contains one or more SCSI Target Ports and one or more device servers and associated logical units. For iSCSI, the SCSI Device is the component within an iSCSI Node that provides the SCSI functionality. As such, there can be at most, one SCSI Device within a given iSCSI Node. Access to the SCSI Device can only be achieved in an iSCSI normal operational session. The SCSI Device Name is defined to be the iSCSI Name of the node.

SCSI Port: This is the SAM2 term for an entity in a SCSI Device that provides the SCSI functionality to interface with a service delivery subsystem. For iSCSI, the definition of the SCSI Initiator Port and the SCSI Target Port are different.


SCSI Initiator Port: This maps to the endpoint of an iSCSI normal operational session. An iSCSI normal operational session is negotiated through the login process between an iSCSI initiator node and an iSCSI target node. At successful completion of this process, a SCSI Initiator Port is created within the SCSI Initiator Device. The SCSI Initiator Port Name and SCSI Initiator Port Identifier are both defined to be the iSCSI Initiator Name together
with (a) a label that identifies it as an initiator port name/identifier and (b) the ISID portion of the session identifier.

SCSI Target Port: This maps to an iSCSI Target Portal Group.

SCSI Port Name: A name made up as UTF-8 characters and includes the iSCSI Name + ’i’ or ’t’ + ISID or Portal Group Tag.

SCSI Target Port Name and SCSI Target Port Identifier: These are both defined to be the iSCSI Target Name together with (a) a label that identifies it as a target port name/identifier and (b) the portal group tag.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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