C6100 - Raw commands for fan speed not working

Hi everyone, 

I have an old Dell C6100 with 4 working blades running Ubuntu 22.04 and I need to manually control fans speed with ipmitool via BMC.

I found a list of raw commands on how to control the server through BMC here, in particular I am interested in the commands listed at pages 35 and 36 to control fans speed.

So to use the commands SetFanControl, the command line should look like this:

"ipmitool -I lan plus ... raw 0x34 0x61 0xB2"

where:

- the first byte 0x34 is required to select the right NetFunction (OEM in this case)

- the second byte 0x61 is required to select the right command (SetFanControl)

- the third byte 0xB2 is required to both enable the manual speed control (7th bit) and to specify the speed desired (bits from 6 to 1).

So in this case, 0xB2 corresponds to 10110010 in binary. From left to right, the first bit (7th) is equal to 1 to enable fan control, the last 6 bits correspond to 50 in dec. So I would expect my fans to run at 50%.

However, this is not working and the fans keep running at 4700 RPM, whereas I would expect them to run up to 6500 RPM which is about 50% of the maximum fans speed (around 13000 RPM).

The terminal seems to accept the command so I guess the syntax should be fine. Also, if I enter the command line:

"ipmitool -I lan plus ... raw 0x34 0x62"

I can verify that the BMC has recorded my request correctly.

I believe there should be something preventing me to have full control over the fans. 

Does anyone have any suggestions? I can provide more details if required.

Any help would be much appreciated. Thanks!