Question OK to use 16x riser cables with molex power input?

[nhprof]

I'm trying to build a multi-GPU unit for machine learning applications, and I'm new to all this. A lot of the design is based upon mining rigs, with a few differences. I suspect that bandwidth will be important for my application, and so I hope to use PCIe 16x connectors between each GPU and the motherboard instead of the USB to 1x card that seems to be common. There will be too many GPU units to run them all off a single power supply, so I have identified a 16x riser that takes 4-pin molex auxiliary power: https://www.amazon.com/Express-Riser-Extender-Molex-Ribbon/dp/B00OTGJQ10?th=1. (I gather that molex can work here as long as you don't combine more than two units on one cable.)

So here's what I'm wondering:
1. Assuming that I power each GPU and its riser from the same PSU, and we have no more than 2 risers on a single molex, is this likely to work?
2. Can I use something like the follwoing for running power to the risers? https://www.amazon.com/Molex-Power-Adapter-Cable-Cards/dp/B005YCISBM. I'm a little suspicious of it given the price!
3. Is there anything I need to know about where the molex plugs into the PSU -- will a 6-pin port labeled for SATA work, or do they not supply enough power?

Thank you in advance for your help, and apologies if my question is overly naive!

Additional information in case it matters: We have a Supermicro M12SWA-TF motherboard (chosen for the number of PCIe lanes it can support) and 6 Nvidia 1080 Ti GPUs.

 

[COLGeek]

Use of adapters like those are generally not recommended. They are often of low quality and can lead to unfortunate failures.

What PSUs do you intend to use?

 

[kanewolf]

I'm trying to build a multi-GPU unit for machine learning applications, and I'm new to all this. A lot of the design is based upon mining rigs, with a few differences. I suspect that bandwidth will be important for my application, and so I hope to use PCIe 16x connectors between each GPU and the motherboard instead of the USB to 1x card that seems to be common. There will be too many GPU units to run them all off a single power supply, so I have identified a 16x riser that takes 4-pin molex auxiliary power: https://www.amazon.com/Express-Riser-Extender-Molex-Ribbon/dp/B00OTGJQ10?th=1. (I gather that molex can work here as long as you don't combine more than two units on one cable.)

So here's what I'm wondering:
1. Assuming that I power each GPU and its riser from the same PSU, and we have no more than 2 risers on a single molex, is this likely to work?
2. Can I use something like the follwoing for running power to the risers? https://www.amazon.com/Molex-Power-Adapter-Cable-Cards/dp/B005YCISBM. I'm a little suspicious of it given the price!
3. Is there anything I need to know about where the molex plugs into the PSU -- will a 6-pin port labeled for SATA work, or do they not supply enough power?

Thank you in advance for your help, and apologies if my question is overly naive!

Additional information in case it matters: We have a Supermicro M12SWA-TF motherboard (chosen for the number of PCIe lanes it can support) and 6 Nvidia 1080 Ti GPUs.

I am betting that extender is rated for PCIe 1.0. It looks like garbage hardware to me.
Do NOT use any adapters to the PCIe power on your graphics cards. If you don't have the proper connectors, then you need a different power supply.

 

[nhprof]

Thank you for the replies! You have confirmed my suspicion that this would be a sketchy solution. Unfortunately, I have not been able to find any other product that will allow for 16x connection with power. I may have to fall back on 1x after all.

I haven't yet bought any PSU, since I don't yet know what connectors I will need. The tentative plan is to get a 1KW unit for the motherboard and two GPU, and a 1.2KW unit for the remaining four GPU. Based only on pin count, something like the Corsair-RM1200x-Shift seems to have enough connection points, if it's ok to power a riser off a plug labeled for SATA. If that's not ok, then I may need to split the load onto three PSU.

 

[COLGeek]

Depending on the application, you may not need the full bandwidth of a x16 slot.

The motherboard will provide up to 75 watts via the PCIe slots and your PSUs will provide the external power to the GPUs. Once connected, as you propose, you should be okay, from a power perspective.

If you use risers, do you have a solution to mount that many GPUs?

Are you firm on the use of 1080 Ti GPUs?

There are single slot workstation solutions that may be more suitable:

NVIDIA RTX A4000 Graphics Card

Engineer Next-Generation Products, Design Cityscapes of the Future.

www.nvidia.com

 

[kanewolf]

Thank you for the replies! You have confirmed my suspicion that this would be a sketchy solution. Unfortunately, I have not been able to find any other product that will allow for 16x connection with power. I may have to fall back on 1x after all.

I haven't yet bought any PSU, since I don't yet know what connectors I will need. The tentative plan is to get a 1KW unit for the motherboard and two GPU, and a 1.2KW unit for the remaining four GPU. Based only on pin count, something like the Corsair-RM1200x-Shift seems to have enough connection points, if it's ok to power a riser off a plug labeled for SATA. If that's not ok, then I may need to split the load onto three PSU.

Why do you need power on the riser? The motherboard slot will supply power.

 

[nhprof]

I am committed to the 6x1080 Ti GPU; we have them on hand as a result of a grant.

My understanding is that relying on the motherboard for power only works if the whole system uses a single PSU. Otherwise, if you want to rely on multiple PSU then you need to ensure they are isolated from one another, meaning that the riser needs its own power attached to the same power supply as the corresponding GPU. I haven't yet come across a PSU with enough plug connections to handle the whole system, hence my reason for looking into configurations using multiple power supplies.

I'm planning to mount the GPU units on an open frame mining rack.

 

[COLGeek]

I am committed to the 6x1080 Ti GPU; we have them on hand as a result of a grant.

My understanding is that relying on the motherboard for power only works if the whole system uses a single PSU. Otherwise, if you want to rely on multiple PSU then you need to ensure they are isolated from one another, meaning that the riser needs its own power attached to the same power supply as the corresponding GPU. I haven't yet come across a PSU with enough plug connections to handle the whole system, hence my reason for looking into configurations using multiple power supplies.

I'm planning to mount the GPU units on an open frame mining rack.

Are we to assume this is an AI/LLM project?

 

[nhprof]

Yes. Did I post it in the wrong forum? Apologies if so.

Are we to assume this is an AI/LLM project?

 

[COLGeek]

Yes. Did I post it in the wrong forum? Apologies if so.

No, this is fine. Just thinking through the x16 vice x1 riser consideration.

I would not use Molex powered anything. Something using SATA power and a kit designed for mining applications would likely do the trick.

https://www.amazon.com/FebSmart-Bit...Cable-GPU-Adapter-Ethereum/dp/B07GJNMLYM?th=1

There are adapters to allow two PSUs to be interconnected for use in systems like you are building:

https://www.newegg.com/battleborn-1...MKP-PC-_-pla-_-Data Adapters-_-9SIA85V3DG9612

This rig is going to generate a fair amount of heat and noise. I hope you have taken that into account in your build plans.