Adding a second M.2 to an X370 board

[Mr Technician]

I'm running a Ryzen 3600x on an Asus Crosshar VI Hero motherboard (X370) and am considering add a second M.2 drive using a PCIE adapter. My understanding is this would run off the four lanes that run to the chipset (16 GPU + 4 directly to m.2 + 4 to chipset). Would this be likely to cause performance issues?

[mariushm]

The pci-e lanes created by the chipset are pci-e 2.0, meaning each lane is capable of 500 MB/s  , so a pci-e x4 slot will give you maximum 2 GB/s in either direction.

 

The x370 chipset creates 8 pci-e lanes but it's up to the motherboard maker how it arranges the pci-e lanes ... usually 4 go to the bottom pci-e x16 slot (so electrically x8), and 2 or 4 to a 2nd m.2 connector.

Sometimes 2 lanes are shared between the pci-e x16 (x4) and the m.2 connector - if you put a ssd into 2nd m.2, then pci-e x16 (x4) could be downgraded to x1 or x2.