Forgot to mention - I pointed Lenovo at this thread, but got the usual "OS isn't supported, find an alternative"

I have recently purchased four SR635v3 servers with AMD EPYC 9354P cpu.

I managed to get some info from Lenovo about how to manually change the fan speeds.

How to get the existing fan speeds. If this fails, check IPMI settings in the BMC.

[09:10 xcp01 ~]# ipmitool sdr list | grep -i fan
Fan Mismatch     | 0x00              | ok
Fan 1 Front Tach | 19072 RPM         | ok
Fan 2 Front Tach | 19072 RPM         | ok
Fan 3 Front Tach | 18944 RPM         | ok
Fan 4 Front Tach | 19072 RPM         | ok
Fan 5 Front Tach | 18944 RPM         | ok
Fan 6 Front Tach | 19072 RPM         | ok
Fan 7 Front Tach | 0 RPM             | ok
Fan 1 Rear Tach  | 15768 RPM         | ok
Fan 2 Rear Tach  | 15768 RPM         | ok
Fan 3 Rear Tach  | 15876 RPM         | ok
Fan 4 Rear Tach  | 15876 RPM         | ok
Fan 5 Rear Tach  | 15768 RPM         | ok
Fan 6 Rear Tach  | 15768 RPM         | ok
Fan 7 Rear Tach  | 0 RPM             | ok
Sys Fan Pwr      | 48 Watts          | ok

To change the fans to a fixed percentage - note the decimal "35" this is the percentage of maximum fan speed to set to.

ipmitool raw 0x3a 0x07 0xff 35 0x01

After a short while for the fans to spin down.

Fan Mismatch     | 0x00              | ok
Fan 1 Front Tach | 12288 RPM         | ok
Fan 2 Front Tach | 12160 RPM         | ok
Fan 3 Front Tach | 12160 RPM         | ok
Fan 4 Front Tach | 12288 RPM         | ok
Fan 5 Front Tach | 12160 RPM         | ok
Fan 6 Front Tach | 12288 RPM         | ok
Fan 7 Front Tach | 0 RPM             | ok
Fan 1 Rear Tach  | 10152 RPM         | ok
Fan 2 Rear Tach  | 10152 RPM         | ok
Fan 3 Rear Tach  | 10260 RPM         | ok
Fan 4 Rear Tach  | 10152 RPM         | ok
Fan 5 Rear Tach  | 10260 RPM         | ok
Fan 6 Rear Tach  | 10152 RPM         | ok
Fan 7 Rear Tach  | 0 RPM             | ok
Sys Fan Pwr      | 15 Watts          | ok

To revert to auto-fan control you either need to restart the BMC/XCC controller which isn't system impacting.

Please keep in mind this was stressed to me that its NOT SUPPORTED/RECOMMENDED - and could cause thermal damage to internal components!!

We only have the M.2 mirror kit with two small disks, no other raid cards or internal disks.
If you have RAID and internal disks you might want to fix your fans to a higher speed.

Someone with scripting knowledge could also monitor a few temps and adjust the IPMI fan control accordingly.
This could even be managed externally via IPMI over LAN for multiple servers.