Performance decrease by Using two M.2_Drives and three SATA_ports with 16 usable PCIe_Lane

[imozon]

Useing a Asus_PRIME_Z370-A Mainboard and a Intel® Core™ i7-8700 Processor. Resulting in 16xPCIe_Lanes. If i use a GPU in x8 Mode. And two M.2 Drives in x4 Mode. All 16 Lanes are used. The Mainboard manual notes that using the M.2_1 port will deactivate the SATA6G_1 port. And using the M.2_2 port deactivates SATA6G_5 and SATA6G_6. Leaving SATA6G_2, SATA6G_3, SATA6G_4, active. If i would use this three open ports 2, 3, and 4, for SSD's would they suffer a decrease in performance. Because the GPU and the two M.2_Drives use all the 16Lanes.

If yes.

Would only using one M.2 Drive instead of two solve the performance decrease by leaving x4 Lanes open to use.

[porina]

The M.2 ports are probably connected to the chipset, not the CPU. So the CPU 16x lanes still all go to the GPU, and everything else goes via chipset. If you try to transfer to all the drives at once they might bottleneck as there is dedicated 4x between chipset and CPU from memory.

 

If you get an adapter card, you can put the M.2 NVMe SSDs on the CPU lanes, and only then would it start to take away from the GPU. You're unlikely to feel any difference in doing this. I've tried, with Optane, and it was just detectable in benchmarks for random transfers in that case.

[Sakkura]

The CPU has 16 PCIe lanes, but the chipset offers up to another 24 PCIe lanes.

 

SATA ports do not use PCIe lanes at all, though they do use HSIO lanes.