X399 Motherboards with Bifurcation support?

[royalba94]

Been looking all over the internet for information on this and the only thing I found is that the Asrock X399M supports it but unsure about the rest.

Unfortunately I'm looking for an ATX or EATX motherboard so that rules the one confirmed one out.

Anybody own some of the other mobo options and can check in the BIOS for me?

Any advice/help appreciated!

 

[Aluminum]

All the asrock boards with recent bios versions support their own passive quad NVMe m.2 card which requires x16 to 4x4 bifurcation, so it should work with other things.

Why do you need it though? Every board except the uATX is 2x8 and 2x16. You can also wire up the triple m.2 slots on any TR board to be regular x4 slots with adapters as they are direct from the CPU.

The PCIe controller in TR/Epryc natively splits down to all x4 (max possible) and quite a few x2 (up to whatever root limits) vendor support of course varies.

 

[royalba94]

All the asrock boards with recent bios versions support their own passive quad NVMe m.2 card which requires x16 to 4x4 bifurcation, so it should work with other things.

Why do you need it though? Every board except the uATX is 2x8 and 2x16. You can also wire up the triple m.2 slots on any TR board to be regular x4 slots with adapters as they are direct from the CPU.

The PCIe controller in TR/Epryc natively splits down to all x4 (max possible) and quite a few x2 (up to whatever root limits) vendor support of course varies.

Thanks!

I was primarily wondering because I was hoping to split a x16 into 2 x8 slots for a couple more Raid/HBA/NIC cards which are x8. Also if that worked then it would have given me the option of another GPU later on if I needed it.
You make a good point about converting M.2 to x4 which would give me plenty of connectivity for that level of hardware.

To be honest I'm probably just overthinking things at this point cause if I do run out of slots then I should probably consider splitting the workloads off onto different machines anyway...