About SCSI TID Maps for FC Adapters

Open-Systems Host Attachment Guide

Version
9.8.7
Audience
anonymous
Part Number
MK-90RD7037-31

When an arbitrated loop (AL) is established or re-established, the port addresses are assigned automatically to prevent duplicate target IDs (TID). When using the SCSI over Fibre Channel protocol (FCP), TIDs are no longer needed. SCSI is a bus-oriented protocol requiring each device to have a unique address since all commands go to all devices.

For Fibre Channel, the AL-PA is used instead of the TID to direct packets to the desired destination. Unlike traditional SCSI, once control of the loop is acquired, a point-to-point connection is established from the initiator to the target. To enable transparent use of FCP, the host operating system “maps” a TID to each AL-PA.

SCSI TID map (ScanDown=0) and SCSI TID map (ScanDown=1) identify the fixed mappings between the bus/TID/LUN addresses assigned by the host OS and the Fibre Channel native addresses (AL_PA/SEL_ID) for Fibre Channel adapters. There are two potential mappings depending on the value of the ScanDown registry parameter:

Note: When storage system devices and other types of devices are connected in the same arbitrated loop, the mappings cannot be guaranteed.