MSI Pro Z790-A Max question about lanes and PCIe expansion

[music2024]

I need help with an explanation of expansion possibilities and lanes on a MSI Pro Z790-A Max.

Right now I don't have a separate GPU and am using all 4 M2 slots of nvme which are almost full. So I have been looking at options for adding more NVMEs as they are faster for what I need in music production than sata connected SSDs. I came across NVME to PCIe adapters in single and quad form. For the quad ones, it says that every nvme installed in it needs its own x4 lane. So is it correct that in order to have 4 nvme on a quad adapter that on the Motherboard only the PCI_E1 which is a x16 will be able to do that? But if I did that, then I won't be able to use a good GPU in the future? My plan before really understanding all of this was to put it in the PCI_E3 slot. Based on the manual it says that slot is only a x4. Does that mean for this E3 slot only 1 nvme is possible and if this is the case, I should not even bother with a quad adapter and just get a single one?

Final question, would putting a NVME to PCIe adapter on the E3 slot with a 4TB nvme slow down any of my lanes such as my existing 4 M2 slot nvmes which are connected to the MB? Is there any system wide performance downside to expanding with 1 more nvme through the PCI_E3 slot?

Thank you for any help and explanation of how this works.

 

[citay]

My plan before really understanding all of this was to put it in the PCI_E3 slot. Based on the manual it says that slot is only a x4. Does that mean for this E3 slot only 1 nvme is possible and if this is the case, I should not even bother with a quad adapter and just get a single one?

Correct. The other two long slots are x16 in length, but only wired up for x4 and x1 electrically. The contacts will literally end way before the slot ends, you can see this once you shine a light into those lower slots. So on an x4/x4/x4/x4 adapter card, only the first SSD will get its x4 lanes.

So usually, only the first slot can do this, and then the board needs to have the setting "PCIe Slot Lanes Configuration" for bifurcation, see here. That setting allows it to switch the single x16 lanes to the x4/x4/x4/x4 the adapter would need. Otherwise, the first SSD would take up x4 lanes from the x16 available, but the rest cannot be assigned to the other SSDs. So again, only the first SSD would get its x4 lanes when you don't have that setting on your board. They don't really advertise this setting, so it's even difficult to tell beforehand if a board has it, unless you see a BIOS screenshot of it.

Your board, in the specifications of the manual, does not mention any lane sharing between different PCIe slots and M.2 slots or SATA ports etc., so all the PCIe lanes should be exclusive and not make something else stop working if you use them. If there was lane sharing, that's where they'd mention it.

BTW, technically it would be called an M.2 to PCIe adapter, since NVMe is only the protocol that M.2 PCIe SSDs use. But the adapter makes the M.2 slot format usable in a PCIe slot format, so M.2 to PCIe.

 

[music2024]

Correct. The other two long slots are x16 in length, but only wired up for x4 and x1 electrically. The contacts will literally end way before the slot ends, you can see this once you shine a light into those lower slots. So on an x4/x4/x4/x4 adapter card, only the first SSD will get its x4 lanes.

So usually, only the first slot can do this, and then the board needs to have the setting "PCIe Slot Lanes Configuration" for bifurcation, see here. That setting allows it to switch the single x16 lanes to the x4/x4/x4/x4 the adapter would need. Otherwise, the first SSD would take up x4 lanes from the x16 available, but the rest cannot be assigned to the other SSDs. So again, only the first SSD would get its x4 lanes when you don't have that setting on your board. They don't really advertise this setting, so it's even difficult to tell beforehand if a board has it, unless you see a BIOS screenshot of it.

Your board, in the specifications of the manual, does not mention any lane sharing between different PCIe slots and M.2 slots or SATA ports etc., so all the PCIe lanes should be exclusive and not make something else stop working if you use them. If there was lane sharing, that's where they'd mention it.

BTW, technically it would be called an M.2 to PCIe adapter, since NVMe is only the protocol that M.2 PCIe SSDs use. But the adapter makes the M.2 slot format usable in a PCIe slot format, so M.2 to PCIe.

Thank you so much @citay as once again you clarified a confusing problem. I've asked several technical experts with music computers and the lanes stuff seems to confuse everyone, especially me . So it seems if I want to get a GPU down the line then I need to be content with using only the slot 3 for only one more M2 and any other future needs I'd need to wait to upgrade my existing ones swapped out for larger sizes or make do with the slower SATA connected SSDs.

Thank you for getting back to me on this question quickly as I may have a deadline on this and needed to decide soon. You're a credit to this forum for helping everyone. Thanks.

 

[citay]

Glad to help, you're welcome, and thanks also for your kind words.

 

[Richj44]

Your board, in the specifications of the manual, does not mention any lane sharing between different PCIe slots and M.2 slots or SATA ports etc., so all the PCIe lanes should be exclusive and not make something else stop working if you use them. If there was lane sharing, that's where they'd mention it.

To confirm, I have the same board and can't find any reference to lane sharing / bifurcation in the BIOS.

 

[citay]

Yep, it's not that common for boards to have it. It would be called something like "PCI_E1 Lanes Configuration". My Z590 board had it, my Z690 doesn't.