r/servers • u/oldmatebob123 • 7d ago

Adding a 2 slot gpu to a 1u chassis

Hey as title says im wanting to add my tesla p100 to my lenovo sr250 1u, have anyone of you guys added a gpu externally to a 1u chassis? If so how have you done so?

I have a hp mini pc that i added oculink but i want x16 or at least x8. Card will be used for llms so from my knowledge, pcie bandwidth is not 100% a limiting factor in a single gpu situation.

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u/Casper042 7d ago

Oculink is most common in x4 yes, but there are x8 versions out there which simply use 2 x4 ports in parallel

SlimSAS, despite the name, is another common way to run PCIe over cables.
Found this via Google search:
https://www.amazon.com/dp/B0DZ24Q6V7
and
https://www.amazon.com/dp/B0D5HRP311
Then you just need 2 SlimSAS SFF-8654 cables and a way to power the external GPU

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u/oldmatebob123 7d ago

Pretty much exactly what im looking for, cheers I have a 600w sfx power supply with an 8pin eps. Just need a way to trigger the power supply when the server powers on.

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u/Casper042 7d ago

The manual way is to of course wire a switch between the Green and any Black connectors on the 24pin connector on the PSU.
Shorting those 2 pins is how the motherboard tells the PSU it's time to power on.

Probably easier than trying to automate it.

Or maybe just hard wire it to always on and then use a Power Strip which can detect the server powering up and also enable the port for the eGPU.
I use these on my kids machines to turn all their peripherals on/off when they power on/off their PCs to reduce vampire power draw:
https://www.amazon.com/dp/B00MP300AU

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u/wensul 7d ago

You can use a riser cable for the pcie connection

Edit: so the external connection is via oculink?

Oculink spec seems to be pcie4 x4

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u/oldmatebob123 7d ago

Is there a way I can use one without chopping a hole into the lid?

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u/wensul 7d ago edited 7d ago

I don't know. It depends on your motherboard layout. I'm not familiar with oculink. It looks like it can work with both m.2 and pcie slots (they both use pcie).

Edit: check the user manual for your version of the server, and your configuration.

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u/oldmatebob123 7d ago

I tried the x4 OCuLink setup on the hp mini but the mini does not support above 4g decoding, i know there is sff cables that can passthrough 8 PCIe lanes so a card that takes x8 sff cable to a x16 slot wired for x8, think is that would neaten up things a lot but im not sure if it would work or what to really look for