The basic question is: If there are four PCIe lanes between the CPU and chipset on an X570 motherboard, then how can everything connected to the many chipset lanes be on equal footing with the direct CPU connections?
The context: I have a standard, non-Threadripper 3000 Ryzen on an Asus X570-P motherboard, currently with a single PCIe Gen 3.0 x4 NVMe SSD installed, and obviously a graphics card which needs as many lanes as possible. The existing SSD is sitting in the CPU-connected Gen 4.0 x4 M.2 slot. There is a second 4.0 x4 M.2 slot that is connected to the chipset instead of the CPU (according to both the manual and the diagram below).
Now I would like to install a second SSD, either a Gen 3.0 x4 or Gen 4.0 x4. But I am fascinated and profoundly confused by the lane diagrams of the X570 setup, an unofficial analysis of which can be found here: https://hexus.net/tech/features/mainboard/131789-amd-ryzen-3000-supporting-x570-chipset-examined/
My understanding, and my questions: There is evidently only a 4.0×4 connection between the chipset and the CPU, and then a plethora of lanes from the chipset to everything else. So, if I install a second SSD in the chipset-connected slot:
- It seems obvious the GPU will not be impacted (?)
- The first SSD should also not be impacted (?)
- … but the connection to the new SSD must somehow be slower than the first one, since it is sharing its four lanes with all the other USB connections and whatnot? However, neither the X570-P manual/webpage nor the above webpage mention anything about such a bottleneck. Is the chipset doing some sort of black magic here? Also, conversely, would this second SSD be influenced by peripherals… meaning that e.g. a Gen 4.0 SSD might be rather pointless here?
Best Answer
Yes, you are right, but remember: PCIe gen4 x4 is 8GB/s. It is very, very difficult, to saturate this, even with 2 SSDs. Most SSDs are much slower. Like reading with 3.5GB/s is fast, but that would be 7 of 8GB/s. Still 1GB/s left for USB3 - wich usually is much more than enought. This would saturate at least 5 modern HDDs at the same time. Or almost 2 SATA 3 SSDs.
Don't be affraid of that. PCIe also is much less CPU intensive than SATA - this all contributes to much better real life performance. You will not notice a bottleneck. You could in theory reach it, but it is very, very unrealistic in reality. :D
Have fun with your nice Setup.