I2C, sgpio and fan control

[MisterE2002]

In the current setup i connected my SC846 fans directly to the X11SCL-F motherboard. After some time the fans slow down. But FANA seems never to increase speed on load.

But i also noticed 3 fan connectors on the BPN-SAS2-846EL1 backplane. I did a simple test and connected 1 fan to the backplane. Now it seems to stay in the jet-mode.

I find the manuals of the Motherboard/backplane confusing. I hope i understand it correctly.
Do i need a I2C cable between the backplane and motherboard to make this work? Those fans will show up in the BMC sensors list? (with new names, instead of FAN1..FAN5 & FANA).


And in that case, do i need this cable? It seems not validated if i enter my motherboard. https://store.supermicro.com/4-pin-to-4-pin-i2c-power-cable-cbl-cdat-0674.html

At this point i have only 1 SAS cable between the HBA and the backplane. This has some flatbed-cable attached. I assume this is only used for controlling the led's? Because i managed to turn enable a led.

This flatbed-cable is called a "sideband" cable? But SGPIO/I2C cables are also sideband?


And what can i really do with those SGPIO connectors?

 

[mav@]

FAN1-5 are usually controlled by CPU temperature, while FANA-B by motherboard or I/O cards temperature. BMC/IPMI may have a switch between different fan modes modes, including something like "High I/O", that increases speed of FANA-B.

I've never heard about backplane fans to be controlled by motherboard. SGPIO controls only LEDs and nothing else. Ones on motherboard are part of the chipset's AHCI SATA controller. Sideband on SAS HBA is likely the same SGPIO. I2c may be more universal in theory, it is a pretty universal transport, but I don't know what it implements in practice in case of this backplane.

 

[sretalla]

There are a large number of threads here on fan control scripts which will probably get you closer to your objective of controlling fans based on HDD temperature/load.

Unless you're using proprietary hardware, it's unlikely that you'll find an option to bring disk temperatures into account for fan speeds.

 

[MisterE2002]

Connected to the motherboard they are slowed down after some time. Albeit still a bit loud.
Found this post.

Supermicro 846 TQ backplane PWM headers question ....

I see the the TQ has 4 4-pin fan headers. However, I don't see a data-cable connecting the backplane to the mobo, just power connectors. Who/what controls the PWM functionality? Are there onboard-temp sensors? Am I missing a cable? Thanks! -mox

forums.servethehome.com

Correct. There is an i2c connector on the backplane that you connect back to a SM motherboard that has a backplane i2c connector. Not all of the SM motherboards have them - but if they do and you make the connection then the various sensors on the backplane (power and temp) will be visible in the IPMI sensor data (the SPD table) and the fans will be under the control of the BMC on the motherboard.

Without this connection any fan plugged in to the MB fan headers will spin at full speed (100% pwm duty cycle).

So, my assumption seems correct. Although i do not understand the last line. I think he meant " backplane" instead of " MB" (motherboard)

 

[MisterE2002]

A update. Took a while. Wanted to connect the backplane BPN-SAS2-846EL1 to the X11SCL-F motherboard using the I2C cable.

Tried multiple cable strategies but they al sucked. The backplane connector is directly behind the metal frame. Tried with Dupont jumper cables which are too high. Finally bought the official CBL-CDAT-0674 cable and still is a PITA to install. Manage to scratch my knuckles.

However i needed to extend this CBL-CDAT-0674 cable. Needed at least 50 cm but it is finally connected now. The chassis wall-fans connected to the backplane. And the best part: functionality got worse.
* The BMC does not "see" the fans. Expected new entries (something similar like the FANA, FAN1-4 for the motherboard)
* So if i change the BMC fan policy only the 2 back fans are modified (connected to said FAN motherboard connectors)
* Also expected a temperature entry for the backplane

So, really not sure what is should bring to the table. I verified my extension wiring. Also the connectors are seated correctly.
Open to suggestions.

 

[MisterE2002]

Last update, maybe it will help someone in the future. So the backplane manual is stating:

The I2C connector is used to monitor the power supply status and to control the fans.

Contacted Supermicro. They confirmed it will not do anything, i quote:

According to Fan Connectors section in the "BPN-SAS2-846EL" manual, there is no PWM fan control as Pin# 4 is NC (no connection).
CBL-CDAT-0674 is the wrong cable. According to our FAQ section (https://www.supermicro.com/FAQ/index.php), CBL-CDAT-0674 is not for connecting BPN-SAS2-846EL1, it is for NVMe AOC i2C. Our Storage team confirmed, "BPN-SAS2-846EL1 I2C is used with CSE-PTJBOD-CB2 or CSE-PTJBOD-CB3." Therefore, connection of i2c from MB to BPN has no purpose.

So, the remark of user PigLover on the servethehome community seems incorrect (or not generally true at least)

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