Please help me understand the fan controls of Supermicro MB's

Jul 29, 2019
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Hi there,

I just bought a Supermicro X11SDV-4C-TP8F, and I really like it. The active cooler I bought from Supermicro is extremely noisy, though, and I wanted to have it a bit quieter.

I read lots of blog posts about setting up the upper and lower threshold of the fan speed via impitools, as well as sending raw commands to lower the duty cycle, thus reducing the fan speed. However, this only works if the fan is set to full speed, as it seems that other modes, such as optimal, override my adjusted duty cycle, and I don't know why.

My problem is that I would like to achieve a quieter fan speed, but of course if the CPU gets very hot, I want the fan to spin faster, but to reduce its speed if the cpu get cooler. I do manage to control the fan speed, but if I choose one of the automatic modes (such as optimal), my settings get overwritten, and if I choose full speed, it won't change its speed based on external events.

I am pretty much confused about setting the lower and upper thresholds. Does it affect the fan speed at all, or is it just an alarm? I set my upper threshold to a quieter value, but my fan wouldn't spin slower after that. But I understand that if I set a too high lower threshold, it might spin faster to recover. So this makes me very confusing - is there a way to use these thresholds to achieve getting a quieter fan?

How is the interplay between duty cycle setting via raw mode, thresholds, the standard and optimal modes? My main goal would be, like, if the CPU is over 50ºC, spin it at 3000 rpm. If it is below 50, spin it at 2500. If below 45, spin at 2200.

I might replace my fan to a quieter one, but before that, I am running at full speed and reduced the duty cycle to 0x2, which gives me 2200 rpm and keeps the cpu around 43º C. Not bad, but it could be cooler. And of course, if something crashes and starts to warm the CPU, I'd like the fan to spin faster and get back to 2200 rpm after cooling.

Could anyone help me to make sense of this all?

Thanks,

Francis
 

TerryPhillips

New Member
May 7, 2019
23
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Francis - you are correct, the thresholds are for the alarms themselves. Not nearly as elaborate as trying to build your own temp/rpm curve, but if you'd like to cap the maximum speed of a fan, the "Noctua NA-FC1 4-pin PWM Fan Controller" (Amazon) will do just that...
 
Jul 29, 2019
16
2
3
Francis - you are correct, the thresholds are for the alarms themselves. Not nearly as elaborate as trying to build your own temp/rpm curve, but if you'd like to cap the maximum speed of a fan, the "Noctua NA-FC1 4-pin PWM Fan Controller" (Amazon) will do just that...
Thanks @TerryPhillips! My fan actually came with the LNA adapter, which I could have used. But I am experimenting a bit with ipmitool to cap it by software.
 

EffrafaxOfWug

Radioactive Member
Feb 12, 2015
1,197
403
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How is the interplay between duty cycle setting via raw mode, thresholds, the standard and optimal modes?
As I understand it (I haven't experimented with it heavily), varying the duty cycle only works when the fan mode is set to "Full". In "Optimal" mode, the BMC will try and manage the fan speeds for you.

There's more talk about it over in the reference thread. My fans are quiet enough that I leave mine in optimal mode but I did once write a simple script to change the duty cycle based on HDD temperatures.
 
Jul 29, 2019
16
2
3
As I understand it (I haven't experimented with it heavily), varying the duty cycle only works when the fan mode is set to "Full". In "Optimal" mode, the BMC will try and manage the fan speeds for you.

There's more talk about it over in the reference thread. My fans are quiet enough that I leave mine in optimal mode but I did once write a simple script to change the duty cycle based on HDD temperatures.
Exactly. I want also to leave on "Optimal", but only when noise isn't an issue for me. I believe it works beautifully with the Supermicro fan. With the Noctua, not so much - the fan spins much slower, and the CPU doesn't get as much cooling.