[Article Suggestion] OCU Link - What it is, what you can use it for, problems/expanding, etc?

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eduncan911

The New James Dean
Jul 27, 2015
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Title says it all! I'm typically 5-10 years behind in my Homelab (as that's all we can afford, right?) and I now have an Epyc board with two OCU Links.

Very first thought that went through my head, "You know, @Patrick has some great videos about a new technology or part or slot or protocol, etc. I am sure he's done a deep-dive into OCU Link, and what awesome uses there are and any issues with U.2 adapters and such."

To my surprise, i can't find a single article on OCU Link! Doh!
 

mirrormax

Active Member
Apr 10, 2020
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It can be confusing since different motherboard manufacturers in the same genartion have chosen different connectors, super micro seems to be mostly oculink, gigabyte mostly slimsasx4, tyan slimsasx8, Asus I've seen both oculink and slimsasx8. Luckily cables/adapter for all connectors and fairly easy to get.
 

eduncan911

The New James Dean
Jul 27, 2015
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Thank you all for the replies. Btw, AsRock Rack seems to use OCU Link in Epyc Gen 1/2 boards.

From an OCULink-on-my-PCIe-3.0-motherboard newbies perspective, here's what I've had to do to educate myself on OCU Link...

OCU Link is one type of connector for PCIe direct connection. Cool, but what can I connect?

First, I had to find out what type of connector there is on the AsRock Rack motherboard. That took a long while, and I finally stumbled over that the protocol that fast devices use for this connector was pre-released and finally renamed to U.2. ok, finally, I know what U.2 is.

Except, oh, this is a PCIe 3.0 motherboard. And there are PCIe 3.0 and 4.0 devices. Rutt rough. And then there's U.2 PCIe 3.0 drives available, and now 4.0. And there may be a different connector preferred for OCU Link 2. I still don't know the backward compatibly of PCIe 4.0 U.2 devices to 3.0. I'm hoping they are backwards compatible, like normal PCIe. Etc.

And then I found U.3... ugh.

The request for the article is to save the next person like me from spending hours across days figuring out this maze of connectors, cables, protocols, speeds, and devices.
 

mirrormax

Active Member
Apr 10, 2020
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Yes u.3 is next level of confusion because there are both backwards compatible and not u.3 devices out there. And it's uses the same sff 8639 connector but with slightly different pinout than u.2, I have a Samsung u.3 name that only works with a u.3 cable(it does say so on the disk itself but I was hoping it might still work in a u.2 8639 enclosure)
 
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eduncan911

The New James Dean
Jul 27, 2015
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eduncan911.com
And then I found this thread...


Yeah, uh, what the frack is going on in the world of drive cables? My head is about to explode.

Can't everyone just pick a single fast interface, and get along? Full height and LP variants? And now I see the old problem of proper right angle and exit of cables, like the old scsi cables and those low profile connectors on some motherboards from back in the 90s.

I really have no idea what article to ask for now. OCU Link 1/2, but really you want U.2 from SlimSAS, but it's not SAS, but you can get SAS cables...
 

NateS

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Apr 19, 2021
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Sacramento, CA, US
Yeah, I think an article that could be very useful would be something like 'NVMe connection options', which looks at all the complexities of U.2/M.2/U.3/EDSFF/etc, the backplane vs direct attached cable options, the switch-based HBA/bifrucation HBA/tri-mode HBA/HW NVMe Raid card options, different PCIe generations and the possible need for retimers for longer cable length, and all the cables and connector types that you might need to wire it all up. There's so many options at this point that an overview could be very useful for people trying to quickly decide what makes the most sense in their systems.
 
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