I recently picked up a server that came with a OCulink backplane and a OCulink card. However it was missing the cable to runs between them. I haven’t played around with OCulink very much. So i am unsure what i need to get this setup working.
OCuLink comes in 4i and 8i versions, 4 lanes and 8 lanes respectively - the 8i is just wider. The backplane looks like 8i. I haven’t used that combo, but I’d imagine you’d need something like: Oulink (SFF-8611) 8i to Oculink (SFF-8611) 4i 2-Port Y Cable
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Are those normally bidirectional?
Yes, they’re just 8 separate PCIe RX+TX lanes. How the host/device uses them is up to them.
I just noticed that the one I linked was 50cm, which is might be a lot longer than most cases need - I’d recommend using one which is as short as possible but still have enough length for turns - you’d get better signal integrity. Not so much a problem for PCIe gen 3, but PCIe gen 4 over 50cm will be … unlikely.
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I will have to see if i can find a shorter cable. But it doesn’t look like anyone sells anything under 50cm. I only need like 15cm. 
I couldn’t get it work. I have tried a 2 different cables. Also tried m.2 to OCulink adapters. So i think my backplane is bad or the cables don’t work in that direction.
Also tried on 2 different motherboards. Bifurcation works with other x8 cards. So not a bios issue.
I will probably swap the backplane with a sata/sas one.
I assume you already read the manual for the HBA
What stands out to me, is that the card is an HBA, and there’s a lot of jumpers to configure it’s behavior.
From the manual, it looks like JP 1-3 are for the card’s SMBus address, and JP5 is for whether it runs in 2x4 or 1x8 mode - which I guess depends on the slot configuration that it’s plugged into and what you’re working with on the BIOS side for whichever slot (is it already bifurcated, or not?)
The parts list on the SuperMicro site also lists what cables to use with it
https://www.supermicro.com/en/products/accessories/addon/AOC-SLG3-2E4T.php
Something like the “CBL-SAST-1002-1” should work, unless it’s one of those OCuLink to SFF-8639+Power cables?
You can buy cables from SuperMicro Supermicro CBL-SAST-1002-1 13cm OCuLink to OCuLink Cable
The problem is my backplane is OCulink 8i. So a 4i cable wont work. And supermicro doesn’t make or sell a Y cable.
I think that the previous owner of the server i got. Sourced the wrong combination of HBA and backplane. So i will need to get an HBA with an 8i port and cable.
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