Asus X570-PLUS (Wi-Fi) M.2 Slot Speed Difference?

Asus X570-PLUS (Wi-Fi) has two pcs M.2 Slot. Both of them are PCIe 4.0 x4.
I have two pcs 2TB Corsair PRO Hydro X Edition with Corasair Liquid Cooling.
(7000 MB/s READ, 6550 MB/s WRITE)

The top M.2 slot 6160 MB/s READ and 6621 MB/s WRITE.
The bottom M.2 slot 6075 MB/s READ and 6229 MB/s WRITE.
I use the latest CrystalDiskMark for testing NVMe speeds.

I changed the location of the NVMe drives.
The bottom M.2 slot shows lower performance again.
Now, I’m sure NVMe drives has no any problem.

The second thing is bios of the motherboard.
I was using the latest bios: version 0820 - 2021/04/28
I also tested the previous bios: 0811 - 2021/04/07
Nothing changed.

The problem maybe any driver ? I made a fresh windows installation.
I tested the speeds without any driver installation. Nothing changed.

NO Driver problem.
NO NVMe SSD problem.
I’m not sure bios of the motherboard problem ???

What should i do now ? Any suggestion ?

the two M.2-Ports have different connections to the cpu.
Read here:
External link:

From what I could read, 3rd gen Ryzen CPUs have 24 PCIe lanes. 16 lanes for PCIe ports*, 4 lanes for one of the two m.2 slots and 4 lanes to communicate with the x570 chipset. Then the x570 chipset “splits” (or “forks”) these 4 lanes into 16 in order to connect to everything else from USB ports, audio chip, etc…

It seems like the top m.2 port (the one without a heatsink) is the one m.2 port directly connected to the CPU while the bottom m.2 port (covered with a heatsink) is connected to the chipset. Please correct me if I’m wrong.

1 Like

may be a cheap pcie->m.2 - Adapter is the cheapest solution for you?

Or, while doing nothing then plotting: deactivate EVERYTHING on your MB like Ports, Audio, USB you dont need etc…tis COULD increase the performance of the slower M.2-Port as i saves some PCIe-Bandwith

Not sure I really understand the problem here. The difference is marginal and in any case it will not affect your plotting because you wont be using anything close to that speed while plotting.

The difference is most likely caused by what is mentioned above, one slot is connected directly to the CPU the other uses the shared lanes of the Chipset.

1 Like

I checked the bios settings. I disable almost everything but nothing changed.
M2_1 LINK is set to GEN 4
M2_2 LINK is set to GEN 4
S LINK is set to GEN 4 (READ and WRITE speed of bottom M2 slot
is 800-850 MB/s if you change it.) Besides, it is so interesting top M2 speed is lower than usual if you choose anything than GEN 4 but it is over 6000 MB/s

you could check the smart-data of the m2’s. Maybe the slower SSD gets slightly warmer and throttles down earlier. Maybe because of fans-positioning in the Tower etc.

I have already checked it. Both SSD has liquid cooling system.

This is the cause here. The M.2 will need to contact the chipset before contacting the processor. Ryzen boards do not have enough PCIe lanes to have 2 M.2 drives run parallel. So the chipset negotiates with the CPU (and can add features also, like RAID etc). And even at that, the M.2(s) can steal PCIe lanes from the neighboring x16 slot.