I've read many threads related to this issue... but I'm going crazy with the noise these fans generate.
From the quickspecs: operating at 23C ambient temperature the base model is rated at 26 dB - aditional options may result in increased sound levels. That's very apparent, considering the Delta fans (PFR0912XHE) used in these are rated at 71 dB each when running at full speed 11,500RPM (185.5cfm air flow). You've all heard the jet engine take-off sound.
I have the base model, with a single E5-2520 Xeon 6-core @ 1.9GHz. (Fans #2 and #3 exist, #1 and #4 are blanks). I'm running the latest HP image of ESX 6.0, build 3073146. iLO firmware is the latest 2.30 from August 19, 2015. Proliant System ROM is also the latest J02, dated 08/02/2014. In the BIOS, thermal settings are set to "Optimal Cooling"
Add-on cards: Smart Array P420, firmware version 6.68, and HP NC365T quad NIC, firmware 3.19.0
Regardless of cpu utilization, at 23C ambient temperature fan #2 never drops below 39%, and fan #3 never drops below 31%. I've even ran prime95 for an extended period of time one one of my VMs (See ESX CPU usage chart), and the CPU temp never went above 40C. Additionally, the fans remained at 31% and 39% during this time.
I've had a case open with tech support for about a month (this is a production server), and during that time I've taken the following steps (all had zero effect on the fan operation):
1- replaced a non-HP drive in my RAID5 with a HP model (EH0600JDYTL)
2-replaced the non supported HP NC364T network adapter with the supported HP NC365T
3- replaced all RDIMM with HP SmartMemory. (647651-081) 32GB total, 4 x 8GB.
I read here that non HP add-on cards or non HP anything can cause the iLO to increase these fan speeds.
I think something is wrong with how iLO is controlling these fans. Besides never droppping below 31% and 39%, the fan occasionally ramps up and down slightly (sounds like a siren). This has nothing to do with the load of the server, as running prime95 does not cause the fans to ramp up.
Lastly, I see in quickspecs that using RDIMMs require the redundant enablement kit (part# 664046-B21)
Could this be related? We do not have the kit, we have the base non hot swappable 460W power supply.
Any help is greatly appreciated.
Thanks,
-Digo