查看电源和风扇配置：
1 <h3c-S5560>display power 2 Slot 1: 3 PowerID State Mode Current(A) Voltage(V) Power(W) 4 1 Normal AC -- -- -- 5 2 Absent -- -- -- --
6 7 8 [h3c-S5560]display fan 9 Slot 1: 10 Fan 1: 11 State : FanDirectionFault 12 Airflow Direction: Power-to-port 13 Prefer Airflow Direction: Port-to-power 14 Fan 2: 15 State : FanDirectionFault 16 Airflow Direction: Power-to-port 17 Prefer Airflow Direction: Port-to-power
检查交换机风扇配置信息发现交换机风扇的实际气流方向为：Airflow Direction: Power-to-port（风道风向是电源侧进风、端口侧出风）；而配置用户下看到风扇模块的优选气流方向为：Prefer Airflow Direction: Port-to-power（端口侧进风、电源侧出风），两者不一致（交换机风扇反转），导致交换机风扇状态为：FanDirectionFault（风扇方向错误），风扇信号灯告警，交换机SYS信号灯告警。
处理方法：
fan prefer-direction命令用来配置用户期望的风扇模块的风道风向。undo fan prefer-direction命令用来恢复缺省情况。当风扇模块的风道风向和设备当前期望的风道风向不一致的时候，系统会打印Trap和Log信息提醒用户。缺省情况下，设备的期望风道风向为电源侧进风、端口侧出风（power-to-port）。
或者更改用户期望的风道风向为power-to-port， 保存配置，sys信号灯恢复绿色。
1 <h3c-S5560>system-view 2 System View: return to User View with Ctrl+Z. 3 [h3c-S5560]fan pre 4 [h3c-S5560]fan prefer-direction slot 5 [h3c-S5560]fan prefer-direction slot 1 6 [h3c-S5560]fan prefer-direction slot 1 ? 7 port-to-power From port to power 8 power-to-port From power to port 9 10 [h3c-S5560]fan prefer-direction slot 1 pow 11 [h3c-S5560]fan prefer-direction slot 1 power-to-port 12 [h3c-S5560]dis fan 13 Slot 1: 14 Fan 1: 15 State : Normal 16 Airflow Direction: Power-to-port 17 Prefer Airflow Direction: Power-to-port 18 Fan 2: 19 State : Normal 20 Airflow Direction: Power-to-port 21 Prefer Airflow Direction: Power-to-port 22 23 24 [h3c-S5560]save