HP A5830AF-96G User Manual page 13

NOTE:
If you replace a fan tray from a running switch, and the airflow
direction of the new fan tray is different from the former one, the
alarm message System fan airflow direction is not preferred on
slot X, please check it. appears. To eliminate the alarm, replace
another fan tray with the same airflow direction, or use the fan
slot-number
prefer-direction slot { power-to-port | port-to-power }
command in system view to change the preferred airflow direction
of the switch.
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