Question Ssd slower in second m.2 slot?

[shabby]

Just got a pcie gen 4 ssd and noticed in the top slot i get 7.4gb/sec read and 6.6gb/sec writes while in the lower slot i get 6.6gb/sec read and only 3.2gb/sec write. Is this because the top slot gets its pcie lanes from the cpu and the bottom slot from the chipset? Its an asus x570 mobo.

 

[deustroop]

If the on and off CPU lanes are the same generation then you will notice a performance difference only if your application is sensitive to PCIe latency.

What is the difference between the PCIe lanes from the CPU and the ones from the motherboard? Is there a performance difference?

Answer (1 of 5): The pcie lanes for the cpu are the maximum amount of pcie lanes supported on the motherboard. The long pcie slots on the motherboard are x16, and the only pcie devices (with exceptions) that use this amount of bandwidth are gpu’s. So a single gpu takes up 16 lanes, if your cpu is...

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I wouldn't think a difference in such minuscule latency will cause a substantial loss of bandwidth like you report.

 

[shabby]

I wouldn't think either but it did, only reason i'm using the lower m.2 slot is because the mobo has a heatsink for the ssd and it drops the temps around 10c.

 

[deustroop]

I wouldn't think either but it did, only reason i'm using the lower m.2 slot is because the mobo has a heatsink for the ssd and it drops the temps around 10c.

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Try switching the drives between slots. Same difference ?

 

[shabby]

I did, that's how I got those two results above. One result is before I put the os on it but when I switched it later it's the same results.

 

[KentState]

The lower slot has to share the 4 PCIE lanes back to cpu with everything on the chipset. This includes SATA, USB, nic and so on.