Question Which M.2 drive for this motherboard?

[koti74]

I have an Asus ROG STRIX B550-F GAMING (WI-FI) motherboard with two M.2 ports - one is PCIE 4.0 x4 and the second one is PCIE 3.0 x 4. I have a Samsung SSD 980 PRO 500GB running in the faster slot and the slower slot is empty and I want to buy a 2TB drive for it. Do I stick with the specs and buy a PCIE 3.0 x 4 drive (Lexar 620) or should I get a faster PCIE 4.0 x4 drive (lexar 790)?​

 

[Aeacus]

No point spending money on faster drive since PCI-E 4.0 drive will operate at PCI-E 3.0 speeds in PCI-E 3.0 slot.

Best PCI-E 3.0 M.2 NVMe SSD is Samsung 970 Evo Plus.
Review: https://www.tomshardware.com/reviews/samsung-970-evo-plus-ssd,5608.html

I have it as my OS drive, in 2TB size. Solid performance and great reliability.

970 Evo Plus wipes the floor with Lexar 610,
Lexar 610 review, where 970 Evo Plus is also compared against it,
link: https://www.tomshardware.com/reviews/lexar-nm610-m2-nvme-ssd/2

Edit: i see that review is of Lexar 610 while you talked about Lexar 620. I don't know how much Lexar 620 is better than 610, but i don't think it would be much, making 970 Evo Plus still better drive.

 

[koti74]

No point spending money on faster drive since PCI-E 4.0 drive will operate at PCI-E 3.0 speeds in PCI-E 3.0 slot.

Are you 100% sure this is the case? Logic suggests it is but I've had someone who works in storage tell me that a PCIE 4.0 x4 drive could work faster in a PCIE 3.0 x 4 slot than a PCIE 3.0 x 4 drive.
But PCIE 3.0 is not PCIE 4.0 end of story right ?

 

[Bob.B]

I have an Asus ROG STRIX B550-F GAMING (WI-FI) motherboard with two M.2 ports - one is PCIE 4.0 x4 and the second one is PCIE 3.0 x 4. I have a Samsung SSD 980 PRO 500GB running in the faster slot and the slower slot is empty and I want to buy a 2TB drive for it. Do I stick with the specs and buy a PCIE 3.0 x 4 drive (Lexar 620) or should I get a faster PCIE 4.0 x4 drive (lexar 790)?​

If you want the best perf you might want to shop for a ssd that has dram.

The ssd can only run as fast as the slot speed.

 

[Aeacus]

I've had someone who works in storage tell me that a PCIE 4.0 x4 drive could work faster in a PCIE 3.0 x 4 slot than a PCIE 3.0 x 4 drive.

This only holds true when PCI-E 3.0 drive doesn't fully utilize the bandwidth of PCI-E 3.0, leaving some headroom.

PCI-E 3.0 x4 max bandwidth is 4 GB/s. Now, if PCI-E 3.0 drive utilizes only 3.8 GB/s, leaving 0.2 GB/s headroom, then PCI-E 4.0 drive, that usually operates ~6 GB/s, can fully utilize the PCI-E 3.0 bandwidth of 4 GB/s. Hence making PCI-E 4.0 drive in PCI-E 3.0 slot faster than PCI-E 3.0 drive in PCI-E 3.0 slot.

But when PCI-E 3.0 drive utilizes the full 4 GB/s (which PCI-E 3.0 x4 is capable of), then it is equal to PCI-E 4.0 drive running in PCI-E 3.0 slot.

 

[koti74]

This only holds true when PCI-E 3.0 drive doesn't fully utilize the bandwidth of PCI-E 3.0, leaving some headroom.

PCI-E 3.0 x4 max bandwidth is 4 GB/s. Now, if PCI-E 3.0 drive utilizes only 3.8 GB/s, leaving 0.2 GB/s headroom, then PCI-E 4.0 drive, that usually operates ~6 GB/s, can fully utilize the PCI-E 3.0 bandwidth of 4 GB/s. Hence making PCI-E 4.0 drive in PCI-E 3.0 slot faster than PCI-E 3.0 drive in PCI-E 3.0 slot.

But when PCI-E 3.0 drive utilizes the full 4 GB/s (which PCI-E 3.0 x4 is capable of), then it is equal to PCI-E 4.0 drive running in PCI-E 3.0 slot.

Sounds very right, thank you.

 

[USAFRet]

Are you 100% sure this is the case?

That is absolutely the case.

Performance depends on the slowest device in the chain.

Here, the 3.0 port.

You could put a so far non-existant PCIe 6.0 drive in there, and it will still run at 3.0 performance.