Supermicro backplane fan failure.

[Johnyblaze]

So I have a recently purchased Supermicro 847 JBOD and I have a little issue with the fans. It seems the fans that are connected to the rear backplane "spin down" after 15-30 seconds from power on, which makes sense because that's what pretty much all servers do after they POST. I also noticed this because both backplanes have a red "fan fault" LED and as soon as that turns off, the 4 fans that are connected to the rear backplane spin down to a more reasonable tone. The 3 fans that are connected to the front backplane, part number BPN-SAS2-846EL, however, do not spin down and the fan fault LED on the front backplane stays illuminated red, so it must think something is wrong with a fan or fans on the front backplane and thus it never spins the fans down. I checked and re-seated all fan connectors, and swapped around the fans from front to back, and they're definitely spinning, so I'm not sure why the front backplane is not kicking down the fan speed and why it thinks there is a fan fault. Based on the fan swapping it's definitely isolated to the front backplane and not an individual fan. I'm also looking through the manual PDF but am having a hard time figuring this one out.


Does anyone have any idea as to why the front backplane is stating there is a fan fault and in turn is not spinning the fans down when everything seems to be OK? Additionally, is there any way to adjust the fan speed on this JBOD? I just want to quiet this JBOD down as the fans that are not spinning down are very loud! Thanks for any help.

 

[JJ Johnson]

Are you sure it thinks there's a fault? Do those backplanes have no audible alarm? Try unplugging one of the fans to see.

 

[Johnyblaze]

Are you sure it thinks there's a fault? Do those backplanes have no audible alarm? Try unplugging one of the fans to see.

Yeah I'm sure it thinks there is a fault and yeah it has an audible alarm. The audible alarm goes off when you unplug a PSU so I can verify that's working. When I unplug a fan from the rear backplane after a few seconds the remaining fans kick up to full speed and the red LED turns on indicating a fault. The issue is that the front backplane has all fans connected and the red LED fan fault is lip and and the fans are spinning at full speed. I can tel this because the rear backplane fans are much quieter and spinning slower when there is no fan fault condition. It all looks good and is running fine so I'm just stumped.

 

[JJ Johnson]

So you get a light, but no audible alarm? If it were a motherboard, I'd say it's just not completing its boot sequence.

 

[JBark]

On my old SC846, I know the only way to get decent fan control (besides just replacing them with quieter fans) is to plug the backplane fans directly into the mobo, and setting the fan jumpers on the backplane so it doesn't monitor the fan status. I think this is better on the newer models, but they're still pretty loud. SM has a FAQ entry about an 847 which gives a similar answer:
http://www.supermicro.com/support/faqs/faq.cfm?faq=12634

This especially true if it's an old model that only has 3 pin fans. Those tend to not spin down hardly at all, and the only fix I've seen mentioned online is to just replace them all with 4 pin PWM fans running off the mobo.

Though that doesn't really help with the fault. Only thing I'd say to check is if all the fan wiring is properly connected, and there's not a loose cable somewhere. If one of the RPM sense wires for one of the front fans isn't working, that would probably cause it to throw the fault and keep the fans spun up. Maybe a pin or something where the fan headers plug into has been pushed out of place?

Those fan jumpers on the backplane are probably worth looking at as well. It's different on every one, so hopefully the manual actually says something about it. Some have just a single jumper to disable monitoring, and some seem to have a jumper for each fan. Could try disabling the fan monitor and see what that does.

 

[Johnyblaze]

So you get a light, but no audible alarm? If it were a motherboard, I'd say it's just not completing its boot sequence.

Yes that's right. Light but no alarm, and the alarm definitely goes off when a PSU isn't connected so it works. The backplane seems to work fine, though as it detects drives without an issue.

On my old SC846, I know the only way to get decent fan control (besides just replacing them with quieter fans) is to plug the backplane fans directly into the mobo, and setting the fan jumpers on the backplane so it doesn't monitor the fan status. I think this is better on the newer models, but they're still pretty loud. SM has a FAQ entry about an 847 which gives a similar answer:
http://www.supermicro.com/support/faqs/faq.cfm?faq=12634

This especially true if it's an old model that only has 3 pin fans. Those tend to not spin down hardly at all, and the only fix I've seen mentioned online is to just replace them all with 4 pin PWM fans running off the mobo.

Though that doesn't really help with the fault. Only thing I'd say to check is if all the fan wiring is properly connected, and there's not a loose cable somewhere. If one of the RPM sense wires for one of the front fans isn't working, that would probably cause it to throw the fault and keep the fans spun up. Maybe a pin or something where the fan headers plug into has been pushed out of place?

Those fan jumpers on the backplane are probably worth looking at as well. It's different on every one, so hopefully the manual actually says something about it. Some have just a single jumper to disable monitoring, and some seem to have a jumper for each fan. Could try disabling the fan monitor and see what that does.

I'll have to check the backplane for the fan jumpers. I couldn't seem to find any fan control as it relates to the backplanes mentioned in the manual, maybe I can just pull it out for a closer look. Both of the backplanes are the new ones that have 4 pin PWN fans. Good point on checking RPM wire, it's just hard to tell because it's simply a JBOD so I can't see if any RPM signal like I could with a motherboard, or can I and I just don't know how? Yeah at this point if I could just disable fan monitoring maybe they will slow down and that would be good enough for me. Thanks for the tips, I'll reply back with my findings once I play with it again this weekend.

 

[JJ Johnson]

Yes that's right. Light but no alarm, and the alarm definitely goes off when a PSU isn't connected so it works. The backplane seems to work fine, though as it detects drives without an issue.

I took a quick look through the manual. If I'm reading it correctly, a fan failure alert would also be indicated by a blinking light, not a solid one. I'm of the opinion that the backplane is not detecting a failed fan. It's something else.

Maybe you just have a bad backplane. Have you contacted Supermicro? Maybe you can get a replacement.

 

[JJ Johnson]

I'll have to check the backplane for the fan jumpers. I couldn't seem to find any fan control as it relates to the backplanes mentioned in the manual, maybe I can just pull it out for a closer look. Both of the backplanes are the new ones that have 4 pin PWN fans.

See if you can find the backplane model number and do a search. Supermicro also has manuals for many of the backplanes themselves.

 

[Johnyblaze]

I took a quick look through the manual. If I'm reading it correctly, a fan failure alert would also be indicated by a blinking light, not a solid one. I'm of the opinion that the backplane is not detecting a failed fan. It's something else.

Maybe you just have a bad backplane. Have you contacted Supermicro? Maybe you can get a replacement.

The reason I think it's thinking it's a fan failure is based on my testing with the rear backplane. That is, when I unplug the fan on the rear backplane, the remaining fans spin up to full speed and a solid red LED light comes on, that reads fan fault on it. The front backplane has this behavior (solid red LED light, full speed fans) all the time, even when all the fans are connected. I'll email Supermicro and see what they have to say. Beyond this issue regarding the fan fault and full speed fans, the backplane works just fine.