Symptom
Front vs Rear Threshold should reflect the fan specifications, i.e.
- RED labeled fans and Power supplies , Front Sensor Threshold should be less than Rear Sensor Threshold.
- Blue labeled fans and Power supplies , Front Sensor Threshold should be more than Rear Sensor Threshold.
Observed Behaviour:
Based on the fan direction,
- INLET temp is HIGHER than OUTLET temp.
- Blue Fans have low front Threshold.
Expected Behavior
- INLET temp should be lower than OUTLET temp.
- Blue Fans should have a high front Threshold.
From the airflow perspective, the Inlet sensor reading should always be less than the outlet sensor reading. However, in the N9K 9336PQ family, the front panel temperature sensor has some inaccurate readings due to the front panel utilization & configuration, which causes the Inlet temperature sensor reading to be very close, equal, or even greater than the outlet temperature reading.
We should have higher threshold on the front sensor, because with Blue Fan airflow is from rear to front. With Blue Fan cold air is coming over rear sensor and hot air is exhausted over front sensor.
This can give Temperature alarms:
%PLATFORM-1-PFM_ALERT: Mod 1 sensor X has minor temp alarm
Conditions
Cisco Nexus 9K 9336PQ Platform
Further Problem Description
We should have higher threshold on the front sensor, because with Blue Fan airflow is from rear to front. With Blue Fan cold air is coming over rear sensor and hot air is exhausted over front sensor.
