fan speed PWM (4-pin) oscillation

Oct 21, 2015
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Italy
www.opensupport.it
I have a problem with a fan connected directly in mainboard supermicro A1SAi-2750F.

First test i use the generic case fan 4pin (no data spech) the fan speed oscillation up and down
and mainboard give alert.

i buy another fan NF F12 PWM same problem...

I fix temporary with a custom build cable 4 to 3 pin connector cable, but the speed are fixed and more noise.

i read that i use ipmi to setting some parameter but is safe? this parameter change speed fan?
are mainboard specific value?

tnks.
 

i386

Well-Known Member
Mar 18, 2016
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Germany
The fans goes under a treshhold and causes the ipmi/bmc to ramp up all the fans. This "solves" the problem so the bmc goes back to normal mode, the funs run slower. And the cycle start again.

Depending on your use case there are different ways to fix that:
- no/few low rpm hdds/sata ssds & the used fans provide enough cooling: modify the low treshold settings in ipmi
- high rpm hdds/sas hdds or ssds/pcie ssds: use proper fans with high rpms/static pressure < loud!
 

K D

Well-Known Member
Dec 24, 2016
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This happens when you use lower speed fans. I had this issue with Noctuas where the fan speeds went lower than the lower threshold defined in IPMI. Use IPMITOOL to modify the thresholds and you are good to go.

This is what worked for me based on @PigLover 's write up in the resources section. I've used this in various X10 and X11 boards without issue.

ipmitool sensor thresh FAN# lower lnr lcr lnc
ipmitool sensor thresh FAN# upper unc ucr unr

lnr - Lower Non-Recoverable speed
lcr - Lower Critical speed
lnc - Lower Non-Critical speed

unc - Upper Non-Critical speed
ucr - Upper Critical
unr - Upper Non-Recoverable speed


Example :
ipmitool sensor thresh FAN3 lower 150 200 250

Alternatively if you cannot run IPMITool from baremetal you can run the same commands from a remote system

ipmitool -H [hostname or ip] -U [USERNAME] -P[PASSWORD] sensor thresh FAN# lower lnr lcr lnc
 

Rand__

Well-Known Member
Mar 6, 2014
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@K D Does setting the LTR to something below 300 actually work for you?
Mine all accept the command and dont change the threshold - 300 is the lowest that worked (and is considered safe by SM afaik)...
 

K D

Well-Known Member
Dec 24, 2016
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@K D Does setting the LTR to something below 300 actually work for you?
Mine all accept the command and dont change the threshold - 300 is the lowest that worked (and is considered safe by SM afaik)...
I have set it to 200 in an X10SDV-6C board using 2 Noctua F8 Redux fans. The example I posted was the exact command I used with 2 different motherboards.
 

Rand__

Well-Known Member
Mar 6, 2014
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Hm, looks like its working partially only for me;)
But it used to accept not even the LNR value, so better than nothing:)

ipmitool sensor thresh FAN1 lower 200 250 300
Locating sensor record 'FAN1'...
Setting sensor "FAN1" Lower Non-Recoverable threshold to 200.000
Setting sensor "FAN1" Lower Critical threshold to 250.000
Setting sensor "FAN1" Lower Non-Critical threshold to 300.000

ipmitool sensor |grep FAN1
FAN1 | 1000.000 | RPM | ok | 200.000 | 300.000 | 300.000 | 25300.000 | 25400.000 | 25500.000
 

Stephan

IT Professional
Apr 21, 2017
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Bavaria, Germany
For any serious application, I no longer use onboard fan control through IPMI via a super-I/O chip. In my last project I chose bequiet silent wings 3 pwm fans (~200-1000rpm) connected to an Aquaero 6 LT controller and only left the CPU fan to be regulated by the onboard super-io through the PECI interface (very fast and precise). It is expensive and others pay for a whole motherboard of what this costs, but I really dig the degrees of freedom from this solution. For custom built home workstation/server systems >1500USD like mine maybe worth a look. In my case it solved the problem of cooling an LTO5 drive that is in my workstation, but at the same time staying dead silent when the machine is idle.

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