Cisco UCS Chassis Discovery Protocol – Useless?

Recently we added a new Cisco UCS chassis, our Chassis Discovery Protocol is set to 4 however we only had 1 uplink from each FEX (Fabric Extender) or IOM/IO Module as its referred to in the documentation to the Fabric Interconnect on the new chassis.  According to the UCS documentation the chassis should NOT have been discovered:

Chassis cannot be discovered by Cisco UCS Manager and is not added to the Cisco UCS domain.

There is very little available beyond the documentation so I opened a ticket with TAC to confirm the behavior of changing the Chassis Discovery Policy.

Changing the Chassis Discovery Policy from 4 to 1 will have no effect on chassis #1.  The discovery policy is only used when a new chassis is added, changing the policy to one will allow the 2nd chassis with 1 uplink to be discovered properly.  If you were to add a third chassis with 4 uplinks in the future the chassis would only bring up one uplink due to the policy but all that you would do is re-acknowledge the chassis and all uplinks would be added.

Based on the documentation and feedback from TAC I expected to have to change the policy in order for the chassis to be discovered, which I interpreted as SEEN by UCS Manager.  The wording in the documentation does not seem to be clear on this particular setting as my new chassis with only 1 uplink was SEEN by UCS Manager, however it was in a warning state due to “Unsupported Connectivity.”

I selected the option to “Acknowledge Chassis” which brought the configuration state to “Up,” however UCS Manager seemingly could not detect any information about the chassis.  At this point I changed the Chassis Discovery Policy to 1.  As TAC said, nothing changed with my first chassis, all 4 uplinks still appeared as up however I lost connectivity from my FEX to the FI on chassis #2, odd so I changed the policy back to 4, reset the FEX and they came back online, the chassis was discovered and registered with UCS Manager.


So my question, what is the point of the Chassis Discovery Policy?  With it set to 4 from the original configuration the chassis was seen when I enabled the server port on the FI, when I changed the policy to 1 which should have matched chassis 2 it was no longer able to detect the chassis.  Now in hindsight, I may have just been able to reset my FEX/IOM after changing the policy to 1 (downfall of late night maintenance, your brain isnt always firing on all cylinders).  Has anyone had experience with this that cares to share any information?