[j-nsp] Juniper Fan Speeds - J Series

[Chris]

Hi all,

I was just pulling out a list of different things to graph via SNMP and
I came across this strangeness on two J6350's (JUNOS 10.2R3.10). When I
have been pulling the data out to graph, the fan speed seems to jump
between 37,678 RPM and 9,820 RPM. This is consistant on both routers,
and the speed seems to jump about at random. As an example:

root at acc-bdr2> show chassis fan
      Item                      Status   RPM     Measurement
      Jseries CPU fan           OK       9820    Spinning at high speed
      Jseries Chassis fan 0     OK       37678   Spinning at high speed
      Jseries Chassis fan 1     OK       37678   Spinning at high speed

root at acc-bdr2> show chassis fan
      Item                      Status   RPM     Measurement
      Jseries CPU fan           OK       9820    Spinning at high speed
      Jseries Chassis fan 0     OK       9820    Spinning at high speed
      Jseries Chassis fan 1     OK       37678   Spinning at high speed

root at acc-bdr2> show chassis fan
      Item                      Status   RPM     Measurement
      Jseries CPU fan           OK       37678   Spinning at high speed
      Jseries Chassis fan 0     OK       37678   Spinning at high speed
      Jseries Chassis fan 1     OK       9820    Spinning at high speed

Each of those was approximatley 1 second apart.

>From looking at the thresholds the way I am reading it is the fans
should be on the "normal" speed:

root at acc-bdr2> show chassis temperature-thresholds
                           Fan speed        Yellow alarm         Red alarm
Item                     Normal   High    Normal   Bad fan    Normal  
Bad fan
Chassis default              48     54        65        55       
75        65
Routing Engine               55     60        80        80       
90        90

root at acc-bdr2> show chassis environment
Class Item                           Status     Measurement
Temp  Routing Engine                 OK         27 degrees C / 80 degrees F
      Routing Engine CPU             OK         49 degrees C / 120 degrees F
Fans  Jseries CPU fan                OK         Spinning at high speed
      Jseries Chassis fan 0          OK         Spinning at high speed
      Jseries Chassis fan 1          OK         Spinning at high speed
Power Power Supply 0                 OK
      Power Supply 1                 Absent

Both routers report the exact same fan speeds (9,820 and 37,678) which I
find is odd, I though it would have been unlikely that they are both the
same...

Has anyone come across this before? Is this expected behaviour?

The closest thing I have found is KB12718 - "Why am I seeing fan in high
speed mode on J-Series?" - but I belive the actual fan speed is being
reported incorrectly in this case.

Thanks,
Chris