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[MX] Explanation of fan speed thresholds and "CHASSISD_BLOWERS_SPEED_MEDIUM: Fans and impellers being set to intermediate speed" log messages

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Article ID: KB24390 KB Last Updated: 04 Dec 2019Version: 4.0
Summary:

This article provides information about the different fan speed thresholds in relation to the Chassisd syslog messages.

Symptoms:

This information is about the different fan speed thresholds in relation to the Chassisd syslog messages. As different MX platforms use different threshold values for fan speeds, the thresholds mentioned in the document are only applicable to the MX480 and MX960 platforms. 

Feb 7 17:36:12 CHASSISD_BLOWERS_SPEED_MEDIUM: Fans and impellers being set to intermediate speed
Feb 7 17:36:12 [fan_calypso_update_fan_speed] threshold1:0x85858585 threshold2:0x8585 new_speed:0x44000
Feb 7 17:45:32 CHASSISD_BLOWERS_SPEED: Fans and impellers are now running at normal speed
Feb 7 17:45:32 [fan_calypso_update_fan_speed] threshold1:0x85858585 threshold2:0x8585 new_speed:0xbb000
Feb 7 19:46:58 CHASSISD_BLOWERS_SPEED_MEDIUM: Fans and impellers being set to intermediate speed
Feb 7 19:46:58 [fan_calypso_update_fan_speed] threshold1:0x85858585 threshold2:0x8585 new_speed:0x44000
Feb 7 19:53:18 CHASSISD_BLOWERS_SPEED: Fans and impellers are now running at normal speed
Feb 7 19:53:18 [fan_calypso_update_fan_speed] threshold1:0x85858585 threshold2:0x8585 new_speed:0xbb000
Feb 7 23:51:29 CHASSISD_BLOWERS_SPEED_MEDIUM: Fans and impellers being set to intermediate speed
Feb 7 23:51:29 [fan_calypso_update_fan_speed] threshold1:0x85858585 threshold2:0x8585 new_speed:0x44000
Cause:

It is normal for the fan speed to change on a regular basis in the MX Series routers. These logs are not error messages; they were added to let you know when the fan speed is changing.

Solution:

It is normal for the fan speed to change on a regular basis in the MX Series routers. These logs are not error messages; they were added to let you know when the fan speed is changing. If any of the temperatures reach or go above 55°, then the fans are set to the intermediate speed. If any of the temperatures reach 60°, then the fans go to high speed. Once set to intermediate speed, the highest temperature has to drop to 50° for the fan speed to be lowered to normal. These is a 5-degree gap to prevent from fan speed tagging. The fan speed thresholds are:

  • Normal - 50° C or below

  • Medium - 55° C or above

  • High - 60° C or above

The threshold of this intermediate speed is not displayed by the show chassis temperature-thresholds command. This does not coincide with the table below, as the table contains thresholds that are used to determine different states of the system. They really come into play on the MX router when it must be determined whether or not to shut a system down due to OVER TEMP conditions.

The fan speed control uses different thresholds, which is not in accordance with the temperature threshold table due to the fact that it has three speeds and not two, as listed in the threshold table.

user@router-re0> show chassis temperature-thresholds
                           Fan speed        Yellow alarm         Red alarm
                          (degrees C)        (degrees C)        (degrees C)
Item                     Normal   High    Normal   Bad fan    Normal   Bad fan
Chassis default              48     54        65        55        75        65
Routing Engine 0             70     80        95        95       110       110
Routing Engine 1             70     80        95        95       110       110
FPC 0                        55     60        75        65        90        80
FPC 1                        55     60        75        65        90        80
FPC 2                        55     60        75        65        90        80
FPC 3                        55     60        75        65        90        80
FPC 4                        55     60        75        65        90        80
FPC 5                        55     60        75        65        90        80
FPC 6                        55     60        75        65        90        80
FPC 7                        55     60        75        65        90        80
FPC 8                        55     60        75        65        90        80
FPC 9                        55     60        75        65        90        80
FPC 10                       55     60        75        65        90        80
FPC 11                       55     60        75        65        90        80

Modification History:
2019-12-02: Article reviewed for accuracy; format modified for readability
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