It Matters Where You Shove In That M.2 PCIe SSD
Primary Versus Secondary NVMe 1.4 M.2 On X570
SSDs continue to be the fastest improving component, far outpacing CPUs, GPUs and all the other components we would love to be able to buy. Thankfully they are also the least impacted by supply shortages, so you can actually pick them up! We have quickly gone from the first generation of PCIe 4.0 SSDs to the newest generation which uses NVMe 1.4 and connect with a PCIe 4.0 x4 which have boosted random reads from a peak of 5GB/s to 7GB/s.
As most modern motherboards offer at least two M.2 PCIe SSD ports, The FPS Review took it upon themselves to fire up an AMD X570 motherboard to see what performance difference one of these new SSDs displays in the primary port versus the secondary. This is worth investigating as if a motherboard provides two Gen 4×4 sockets, one has to come from the CPU, and one has to come from the chipset.
Their tests with the MSI SPATIUM M480 SSD showed slower performance on the secondary M.2 PCIe SSD port, using the chipset PCIe lanes, as you would expect, however that difference varied greatly depending on what was being done. For loading an application The FPS Review saw a mere 3% difference, nothing you would ever notice when loading your games; file copying on the other hand showed a much larger delta. That performance difference also varied depending on if you were moving a very large file or a number of smaller files of different sizes.
The article is well worth the time spend reading it, as for many users the differences will be negligible, but for workstation users the differences can be 10% or more!
Your Primary M.2 socket and your Secondary M.2 socket are not the same. They may both claim to have PCI-Express 4.0 x4 performance support, but the path to get there, and the lanes they connect to, come from different places.