Why connect the fan to the motherboard ?

[Le Passant]

My question is only on Supermicro Case, and especially for those with the SAS2-846-EL family expander.
On many pictures and in some threads, it seems that Fans are connected to the Motherboard and not to the Backplane. Or, if I'm not mistaken, there are also fan connectors on the Backplane and they are said to be monitored.

So why connect the Fans to the Motherboard and not to the Backplane ?

As, for me, the Fan monitor function on the Motherboard is referred to the CPU or the Case temp and not really to the Drives temp, as the Backplane who would be. No ?

Or is it simply because it is easiest to define the settings in the Motherboard rather than in the Backplane ?

 

[mjws00]

These cases can mitigate a pretty significant thermal load. Not long ago CPU's, RAM, and additional cards generated tremendous heat. So we cool those critical hot components and use the negative pressure to cool the drives implicitly. High temps on mobo components lead to instability and failure. We also used to have many high speed, high rotation drives that ran very hot, and were quite happy to do so. A NAS that sits mostly idle on incredibly efficient chips flips this upside down and cooling is easy. But the boards and cases are still designed to allow for heavy loads and temps. So we haven't changed the model.

This drive temp issue we yammer about here is slightly over done, imho. The google data is interesting, but qualitative numbers on a lightly used, small, system with drives running a few degrees warmer are not really available. Electronically cooler is typically better, but cool drives fail... hot drives fail... everything fails. :)

I'd be careful that cool running drives (i.e where fans don't kick in) don't starve the rest of the system of the airflow it needs. That said, in my 846 the fans are swapped for quieter units, and barely get off idle while all (x10) components stay chilly. I physically swapped out models to hit the drive temps I wanted vs. noise. This is in a cool basement, not 30C ambient temps.

If you find a cool solution using the backplane. Share it. Lots of folks will be interested.

 

[Le Passant]

Of course, if you look the whole thermal load and not only the drives temp (as I've done) .

You use other units ? Which ones ?

Is it possible to use 80 x 80 x 25 fans rather than the 80 x 80 x 38 of Supermicro ?
Can they fit right in the Case ?

 

[mjws00]

I tried most of the flavors of 80mm that were available locally. The 80X25mm fans fit very nicely into the SM plug and play housing. I ended up with the Arctic F8 PWM rev 2. Noctua's didn't move enough air for my tastes. But it is really personal preference, my 846 sits beside my desk and runs near silent and cool. But I normally have only a dozen drives installed with a bunch of ssds... so a higher load might require more grunt. Testing is easy and worthwhile.

 

[pclausen]

My understanding is that having the fans connected to the SAS2-846-EL means they run at full speed all the time (despite that backplane having 4--pin fan connectors). I asked Supermicro about this and they say it is by design. I thought that maybe I could control the speed via I2C but apparently not according the Supermicro.

By having them connected to the motherboard, you can do crude fan adjustment via IPMI (Optimal, Heavy I/I, Full, etc).

What I'd really like to be able to do, would be to control the backplane fans so that the hottest drive did not exceed 40 degrees. I asked about it here, but it looks like it might only work for linux based machines.

 

[Le Passant]

My understanding is that having the fans connected to the SAS2-846-EL means they run at full speed all the time (despite that backplane having 4--pin fan connectors). I asked Supermicro about this and they say it is by design. I thought that maybe I could control the speed via I2C but apparently not according the Supermicro.

By having them connected to the motherboard, you can do crude fan adjustment via IPMI (Optimal, Heavy I/I, Full, etc).

What I'd really like to be able to do, would be to control the backplane fans so that the hottest drive did not exceed 40 degrees. I asked about it here, but it looks like it might only work for linux based machines.

Ok, a wrong idea then. Especially because my Case will be in the living-room with us all the time. The best solution will be to change the Fans for something less louder in a first time.

 

[Bidule0hm]

they run at full speed all the time (despite that backplane having 4--pin fan connectors). I asked Supermicro about this and they say it is by design.

Ok, that's funny (but a shame too) :)

By having them connected to the motherboard, you can do crude fan adjustment via IPMI (Optimal, Heavy I/I, Full, etc).

Yep, crude is the word...

What I'd really like to be able to do, would be to control the backplane fans so that the hottest drive did not exceed 40 degrees

I'm currently designing (well, in fact it's already designed but I re-design a part) a PI controller for 8 fans (2 for the CPU + 6 for the drives) with a watchdog on each fan and other goodies but it's a 100 % discrete electronic solution (I don't want a MCU who can bug/freeze and I'm sick of the "DIY" arduino projects...) so I don't know if you're interested or not.

 

[pclausen]

Sorry, never did catch your reply, but yes, I'd definitely be interested in hearing move about it. Did you get it going by now? Being that I have 3 chassis, it would be great to be able to have the fans adjust speed as needed. I suspect that being a discrete solution, one would dial in each chassis to where the SMART temps would stay just below 40 degrees under load, and then leave it there, or?

 

[rogerh]

Discrete, analogue electronics doing feedback was possible before computers, in the vacuum tube era! Not just before embedded CPUs and before discrete digital chips.

 

[Bidule0hm]

Not yet, I originally used a proportional only design but then I figured that I can fit a proportional-integral design by adding only a few passive components. With the vacations I didn't find the time to finish the integral part of the circuit but I will as soon as I can.

It uses only one temperature sensor that I'll put on the hottest drive but you can easily add more temp channels if you want (it's just some copy-paste). Once the set point is set the controller will do everything he can to maintain the sensor (and the drive it is attached to) at that temperature, so if you set 35 °C the drive will stay at 35 °C regardless of the ambiant air temperature (within the fans limits of course...), in other words if the ambiant temp rises then the controller will run the fans faster to keep the drive at the same temp and vice versa. Same if the drive is doing some work and dissipate more heat.