PCIe Bifurcation

Tony habergham · 13 Feb 2022 at 15:52

I'm considering purchasing something like one of these, or something similar:
https://www.asus.com/Motherboards-Components/Motherboards/Accessories/HYPER-M-2-X16-CARD-V2/
Which should allow up to four PCIe M.2 drives to be hosted on a single PCIe x16 or x8 slot.

However, I understand that this requires your motherboard to support PCIe Bifircation, and after a couple of hours searching I'm still unclear whether my motherboard, An MSI X470 Gaming Plus Max (v3.0) would - I've read it depends on the motherboard, processor, slot position... can anyone advise? The compatible motherboards listed for this particular model are all Asus boards, with nothing particularly special about them I can see. There are also cheaper more generic models available on an auction site of note.

Tetras · 14 Feb 2022 at 22:34

Wow, that chart is a major headache.

It is a different MSI board, but in this video, you can see him play around with this setting, I assume it is what you're looking for?
(35:59, I think it says: advanced pcie subsystem settings)
https://youtu.be/bu9ZD18a9CY?t=2159

My guess would be that the best you'll get in the second PCI-E slot is 2 M.2s.

Quartz · 14 Feb 2022 at 22:44

That motherboard does appear to support bifurcation. Are you putting the card in the first x16 slot and using a Ryzen G CPU? If not then the other slots are x8 and x4 and unsuitable for your purpose as they will allow only two and one M.2 drives respectively even if the board supports bifurcation.

PCIe bifurcation is more a Threadripper thing where you have plenty of PCIe lanes.

Tetras · 14 Feb 2022 at 23:05

Quartz said:
That motherboard does appear to support bifurcation. Are you putting the card in the first x16 slot and using a Ryzen G CPU? If not then the other slots are x8 and x4 and unsuitable for your purpose as they will allow only two and one M.2 drives respectively even if the board supports bifurcation.

PCIe bifurcation is more a Threadripper thing where you have plenty of PCIe lanes.

Afaik, with a Ryzen G there would still only be a max of 2 M.2s, because they're limited to 8 lanes on the primary PCi-E.

Quartz · 14 Feb 2022 at 23:08

Tetras said:
Afaik, with a Ryzen G there would still only be a max of 2 M.2s, because they're limited to 8 lanes on the primary PCi-E.

Wow. I didn't know that; I thought they got the full 16 so you could plug in a proper GPU.

Tetras · 14 Feb 2022 at 23:28

Quartz said:
Wow. I didn't know that; I thought they got the full 16 so you could plug in a proper GPU.

From what I can remember, Raven Ridge and Picasso are PCI-E 3.0 with 8 lanes (on primary), so the PCI-E slot is always half speed.

Renoir and Cezanne are both PCI-E 3.0 with 16 lanes, which is effectively still half the primary PCI-E on the other CPUs like the 3600 or 5600 (because they're PCI-E 4.0).

So, if you plug a PCI-E 4.0 graphics card into a PCI-E 4.0 motherboard with a Renoir or Cezanne APU, you get half the bandwidth.

Though, thinking about it, the Hyper M.2 is only PCI-E 3.0, so maybe with Renoir or Cezanne you would still be able to configure 4x4x4x4 on the primary slot, in PCI-E 3.0 mode.