PCIe bifurcation : pcmasterrace

[-] Godort@lemm.ee 18 points 3 months ago

I'm not sure what hardware you're running, but with my motherboard, to get 4x4x4x4 out of a slot requires sacrificing GPU bandwidth from x16 to x8

to get 4x NVMe drives out of a single PCIe slot without bifurcation you need a card that has it's own RAID controller. These aren't cheap (think ~$500) as they are specialty hardware, but it's a hell of a lot cheaper than a whole professional workstation or server.

[-] seaQueue@lemmy.world 3 points 3 months ago

You don't necessarily need a raid controller, I think a pcie bridge or switch chip will work too. They're still expensive but they're significantly less than $500.

[-] SitD@lemy.lol 1 points 3 months ago

This sounds like a path I could take - just buying a mainboard like that and making it a NAS. Which board do you have there? If it's AM4, I could get a similar one and just reuse my old CPU.

[-] kusivittula@sopuli.xyz 10 points 3 months ago

i don't think you have much options. cheapest = use gpu in x8. you could try an adapter to plug the ssd into sata port, but no idea if that would even work. just for the fun of it, i looked at my 7800x3d specs and under connectivity it states that 24 pcie lanes are usable of a total of 28, but mobo provides an additional 8 or 16 more depending on the chipset. wondering if that results in 32 or is it limited to 28...

[-] fuckwit_mcbumcrumble@lemmy.dbzer0.com 8 points 3 months ago

It’s all down to your motherboard. But the tldr is no, at least not without compromises.

The top x16 slot is almost always connected directly to the CPU. The others are limited to X8 or X4.

Your CPU has 20 lanes. 16 for the GPU, and 4 for your “main” NVME SSD. Your chipset typically has like 4 or 8 more (the very bottom slot). And you have to figure out some sort of combo where that works, and they’re not combineable. What’s worse is a lot of motherboards hard wire those extra x4 pcie lanes to the M.2 SSD slots so you get no choice.

[-] SitD@lemy.lol 2 points 3 months ago

ur “main” NVME SSD. Your chipset typically has like 4 or 8 more (the very bottom slot). And you have to figure out some sort of combo where that works, and they’re not combineable. What’s worse is a lot of motherboards hard wire those extra x4 pcie lanes to the M.2 SSD slots so you get no choice.

I've put the bifurcation card next to the CPU now and it only offers two x4 lanes. I thought zen2 should be able to handle bifurcation, so if it was directly hooked up with the CPU, I should get all four. Seems chipsets still have some influence over the first PCIe slot.

[-] fuckwit_mcbumcrumble@lemmy.dbzer0.com 2 points 3 months ago

What mobo do you have? That's the most important thing here. Your mobo will almost always be the limiting factor in bifrucation.

When I was looking around before I saw that Asus supports 4 way bifrucation. I got bored so I asked chatGPT and it thinks only two x470 mobos support 4 way bifrucation. ASUS ROG Crosshair VII Hero (Wi-Fi) and MSI X470 Gaming M7 AC. It also seems to think x570 has better support, but I think that's more just that they support two way vs no bifrucation at all.

4 way bifrucation isn't a very common thing for a regular user to do which is probably why so few boards support it. 4 way plus a full fat GPU is even less common. To be honest I'm kinda surprised any 400 series boards support bifrucation at all.

[+] _bcron@lemmy.world 7 points 3 months ago* (last edited 3 months ago)

[deleted]

[-] SitD@lemy.lol 2 points 3 months ago

as x4/x4, but PLX would divvy it all up essentially 4x M.2 at x2/x2/x2/x2, that kinda thing. If this adapter doesn’t have it and you can’t get this to work, and you’re willing to blow another hundred bucks, that other kind of adapter would def work.

Without knowing your motherboard I’d def download the manual and ctrl+f some promising keywords such as ‘bifurcation’ or ‘PCI’ and basically hunt for anything in the manual that describes settings to enable this. Sometimes on a 3 slot board the bottom ‘chipset’ slot can be toggled to run something different than PCH, like some other controller.

I’d also try running the adapter in every possible configuration, on the most current supported PCI-E standards and a previous generation if motherboard allows, ie: adapter top slot, GPU middle slot, GPU top slot, adapter 3rd slot (if mobo has one), disable PCI-E 4.0 or enable 3.0 each time just to see if some configuration works (kinda tedious but costs 0 dollars so

Thanks for the hints. I'll try to put it in gen 3.0 mode and see if I get more settings there, good idea!

[-] hohoho@lemmy.world 6 points 3 months ago

What’s the motherboard model? Which slot are you attempting to use? Is it a physical X16 slot with only a X8 connection? Do you have any other slots available for M.2 drives?

[-] SitD@lemy.lol 1 points 3 months ago

It's a MSI X470 GAMING PRO. Tried both upper x16 slots. The second one seems to be x8, but the first one doesn't work either despite being x16. I have other m.2 slots but they're already used up - however those are smaller SSDs so worst case I could move my OS to a SATA drive and populate those m.2 slots with the larger and newer SSDs that i bought! 😂

[-] Eutent@lemmy.world 2 points 3 months ago

if it fits in the slot, it would surely work

If you got something like the ASUS Hyper M.2 x16 Gen 4 Card:

https://www.amazon.com/ASUS-M-2-X16-Expansion-Card/dp/B084HMHGSP

https://www.asus.com/us/motherboards-components/motherboards/accessories/hyper-m-2-x16-gen-4-card/

Then there are specific motherboards listed that support the bifurcation requirements.

Of course, if your x16 slot is taken up with this thing, you can no longer use the slot for a graphics card.

Perhaps the cheapest way forward would be to use your x16 slot for graphics, and distribute your 4 M.2 cards using multiple adapters in the smaller slots (if you have room for that). One of the adapters might need to be PCIe x1. Well, cheaper than Threadripper!

[-] SitD@lemy.lol 2 points 3 months ago* (last edited 3 months ago)

That's precisely the SSD PCIe solution that I bought. ^^ Yeah, might have to redistribute... Thanks for letting me know about the compatibility listing, I wasn't aware of it. I'll check if I can get one of those second hand.

Edit: I'm slightly worried about ASUS as a mainboard supplier though because of their recent rootkit escapades...

PC Master Race