I recently installed a dell poweredge R7515 however I’m struggling to understand and control the fan curve. I would like to minimize the fan speed to reduce noise.
The fans ramp from 22% to ~40% (~3840 rpm to ~7000 rpm) seemingly at random, even when the system is under minimal load.
I plotted the fan speed and temperature output and provided the results in tabular form below. Fan speed and temperature are from iDRAC. Usage data is from Proxmox.
As you can see, over the course of 40 minutes, the fans ramp from 22% up to 41% and then return to 22% with no apparent change in system load or temperature readings.
Time
09:02:00 AM
09:23:00 AM
09:24:00 AM
09:36:00 AM
09:42:00 AM
Avg Fan Speed
22%
41%
31%
23%
22.67%
CPU1 Temp
50
50
50
50
51
Inlet Temp
28
28
28
28
28
GPU Temp
62
61
61
63
62
Exhaust Temp
46
39
40
46
46
DIMM Temp
49
50
50
53
54
Over the course of the 40 minutes, the maximum CPU usage was <1.4%. Ram usage was 132/256 GiB (128 GiB is assigned to TrueNAS as zfs cache). Server load was <1.6%. There was constant network traffic of 10-30MB/s (over the integrated 1Gb NIC) due to an active Rsync task.
Is this the expected behavior for poweredge systems? I recognize noise is not a primary concern for this platform, but I am still surprised that there does not seem to be a clear cause-and-effect here. Please let me know if you have any recommendations, or if there is any additional information I can provide to help troubleshoot.
I didn’t check any of the numbers, but when I recently got a used Dell workstation, it had a tiny bit of fluctuation like you mentioned. I had been watching upgrade videos and saw there was a fan curve setting in BIOS, which I believe I set at 24% minimum. An almost imperceivable increase in noise from about 2 feet away stopped the occasional peaks in fan speed.
One thing I’ve noticed is that the commanded % and actual fan speed as a percentage of it’s maximum speed will often vary. My ebike has the same problem with the hall effect input, and something tells me that making an ultra precise throttle would be futile if the controller doesn’t have that much resolution. I get the impression from running fans at lower speeds that sometimes the commanded % causes an unexpected amount of change and it may overcompensate.
I do know that the Dell machines expect specific RPM minimums and I believe there is a fan diagnostic test to make certain they are at least making that minimum, so you might want to start there.
thanks for the response KleerKut! Just to make sure I understand, the idea is that the current minimum fan speed (22%) is slightly too low, so the system sporadically receives a command to ‘increase fan speed’. When the ‘increase fan speed’ command occurs, the controller overshoots a reasonable fan speed until it readjusts? So increasing the minimum fan speed slightly should be enough to prevent the ‘increase fan speed’ command from getting triggered in the first place?
I’ll try increasing the minimum fan speed from 22% to 27%.
Interestingly, even the acceptable values for ‘minimum fan speed’ value seem to bounce around slightly. The iDRAC interface will occasionally accept values as low as 14%, but at the moment it will only accept values >=22%. I suspect this might be a function of inlet temperature based on Figure 2 in the Custom Cooling Fan Options whitepaper
Correct. The default slider setting was at 0%, and briefly looking in BIOS showed it asking for as low as 21%, and bouncing beyond 35% occasionally in the short time I watched it. During small fluctuations asking around 21-24%, but the actual RPM reported was changing more than 3%. Then it acted like a cold car where the idle RPM kicked up a bit occasionally.
Like in your case, I wasn’t so much worried about the sound. I had tried a few benchmarks and each of them starting from cold took a while for the fans to catch up. One got to the point the CPU was a few degrees short of thermal throttling. Nothing else stressed the system like that, but I figured increasing the base RPM would help. That’s when I noticed the RPM seemingly dropping down and getting bumped up like starting up a cold car. When I moved the slider up to 24% it stopped doing going through that cycle. The second benchmark attempt kept the max temp about 6C lower.
Thanks for clarifying KleerKut! That makes perfect sense, and the behavior you’re describing is consistent with what I was observing.
I’ve been keeping an eye on fan speeds and system temperatures since updating the minimum default value yesterday; so far I haven’t seen the fans ramping up, but it was very sporadic so I’m not sure if I can say for sure it’s resolved yet. Fingers crossed it continues to behave, as this is a really simple solution.