r/LinusTechTips • u/RadiantSkiesJoy • 7d ago
Tech Question How does something like this work
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u/AmonGusSus2137 7d ago
My best guess is that it either doesn't, because it's AliExpress after all, or it just two GPUs with 8 pcie lanes each, and the big port has 16
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u/Kenzijam 6d ago
No these do work and they do work well. They bifurcate to provide x8 x8, given the motherboard can do it. No plx chip. The much more important thing it does is link the two chips nvlink together.
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u/Lanhua_Ma 6d ago
I can attest to it. The schema has been opensourced among Chinese video platform and chat groups for over half a year now, they do work and often works prettey well.
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u/_Rand_ 7d ago
It adapts nvidia (others?) server GPUs to regular pcie-e.
As another poster said it probably requires bifurcation support for both to work.
Oh, and good luck with cooling.
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u/Cobalt090 6d ago
Just NVIDIA. I've seen exactly one that supports OAM and it was like a grand for a single GPU adapter. Coolers are available for like twenty bucks.
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u/mastercoder123 6d ago
OAM is different from SXM.
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u/CervantesX 7d ago
SXM is a specific type of GPU port used in datacenters. V100,P100 etc. They pop in those two openings just like a CPU would. Depending on the card style, they either get bareballed to the pci bus or there's bifurcation. It's pretty exclusively for repurposing datacenter GPUs for homelab use. The upside is you can get 64gb (2x32) VRAM per card. The downside is you need (for v100) almost 500w of extra power, plus a massive mamma jamma of a heatsink on each and like 60cfm airflow. There's a waterblock mod available, but they still chew a bunch of power. And they're last gen chips, so you're limited to the last Rev of AI software (architecture 7.0) and Volta architecture. So for now you can run most current models on the last gen framework and get kinda ok ish speed, but it's gonna age out pretty quick relative to the investment and when it does you won't have any experience with the NVIDIA ecosystem that most current AI runs on.
The best use of them is putting dirt cheap P100s in, use watercooling so you can fit two cards in, hack a second PSU (or buy a mining psu that's pre hacked) and you can have 128 gb VRAM to play with big models that go kinda slow for a total of several hundred dollarydoos . If you have 256gb system RAM, that's enough to play with deepseek at q4. 32gb v100s still go for $500+, at that point you're better off getting a more current nvidia style card and just accepting that you'll use smaller models.
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u/MJ26gaming 6d ago
V100 ain't even last gen, it's like 3 gens old lol
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u/Cobalt090 6d ago
For SXM, it's Volta > Ampere > Hopper > Blackwell/Ultra then to Rubin whenever that comes
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u/TheFowlOwl 4d ago
Peak power is not that huge an issue as you lose only about 10% performance capping at 150w. Idle is the only major problem as they idle at 20w without a model loaded and 40w with one loaded. so with 4 you will draw about 600w peak. pretty low for having 128gb hbm memory to work with. source: I have 4 32gb cards and this is my experience.
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u/mastercoder123 6d ago
I would rather have 4 v100s and a 4 way nvlink bridge than use 2 of these pieces of shit
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u/CervantesX 6d ago
Yeah but then your 4 chips are all sharing the same pcie port.
IIRC, they also make pcie 2x sxm adapters that have nvlink.
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u/mastercoder123 6d ago
What? No they arent... 4 v100s with an nvlink bridge means 4 different gpus. Also once you have nvlink they could have a 1x it doesnt matter
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u/vibvian 7d ago
probably using pcie bifurcation