That speed is surprising to me considering that the EPYC is supposed to have 128 PCIe lanes. I think that you should check the motherboard manual, if you have o

That speed is surprising to me considering that the EPYC is supposed to have 128 PCIe lanes. I think that you should check the motherboard manual, if you have one, or contact the manufacturer, and see how the board's PCIe is laid out. An EPYC has no need to share PCIe lanes through a PCH and shouldn't have one for the NVMe drives. It's possible that by placing cards in different slots you could gain more speed. There may also be some sort of setting to configure PCIe between 8 16-lane slots (accelerator cards) or 32 4-lane slots (NVMe drives). If you're running a single-threaded application you may be hitting the limits of the DMA and memory controllers.