Which M.2 slot do I use? Does a slot choice affect bandwidth of the SSD and/or GPU?

[Nathanpete]

Building a pretty high end rig sometime in the next 2-3 months (I update my parts list all the time according to prices and new tech), and I know for a fact that I will be using a 1TB M.2 NVME SSD and a 500GB SSD, but I wanted to know which M.2 Slot do I populate? Here are my parts as of right now: (or a PCPP list if u want https://pcpartpicker.com/user/nathanpete/saved/#view=cjpW3C) Ryzen 9 3900X, Asus TUF GAMING X570 Plus Wifi ATX, 4x16GB DDR4-3600, Samsung 970 Evo 1TB, Crucial MX500 SSD, MSI RTX 2080Ti Gaming X Trio, and a SeaSonic Focus Plus 750W 80+ Gold. (This build is for a customer to do Unreal Engine 4 and renderings, along with web browsing and AAA games every once in a while. Current budget tops out at around $3400. If you wish to make suggestions on parts, please do).

So the Asus TUF X570 Plus has 2 M.2 slots (IDK about PCIe Gen 4 support or SATA M.2), but the bottom one has the heatsink, which makes me think it is the one that Asus wants me to populate first. I want to know A) Depending on what M.2 slot I use, will either the GPU or the SSD suffer in performance? Like if I choose the slot above the GPU, will the GPU suffer, and if I put it in the bottom one, will the SSD suffer? Does the 970 Evo even have a need more more bandwidth than the bottom M.2 slot could offer? and B) Would the 970 Evo perform better/last longer/something else positive if I place it under the mobo's M.2 heatsink?

The customer also wants a way to transfer ongoing Unreal Engine 4 projects to a home PC (much less powerful, won't be doing renderings) so he can work from home. My current idea is for him to have a 256 GB USB stick where he can offload projects at the end of the work day, take the USB stick home, and work at home. His home PC may not even have USB 3.1 support, so that is another issue. (I haven't asked him what he knows about remote access or using cloud storage instead, but for now I doubt it.) His home wifi speed isn't very fast so cloud storage will not be fast at all, unless Unreal Engine 4 projects are usually small in size, I have no clue though, never used it. In an environment of slow internet speeds, is a large USB stick the way to go to transfer UE4 projects? My current pick is the SanDisk 256GB Extreme PRO USB 3.1 Solid State Flash Drive with its high R/W speeds. (I base a lot of my hardware picks off of userbenchmark.com, this drive had the highest value score) But you can find a lot of USB 3.0 256 GB sticks for half the price, do I downgrade to a slower or lower capacity USB drive if I don't know if his current PC would be a bottleneck?

[Jumballi]

The slot you chose can have an effect on system performance, on my asus z370 it shares lanes with the gpu and sata and usb 3.1 gen 2. Check the mother board manuals on what lanes it’s shared with. All major retailers make the manual free to everyone.

[Nathanpete]

3 minutes ago, Jumballi said:

The slot you chose can have an effect on system performance, on my asus z370 it shares lanes with the gpu and sata and usb 3.1 gen 2. Check the mother board manuals on what lanes it’s shared with. All major retailers make the manual free to everyone.

The manual (https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/TUF_GAMING_X570-PLUS_WI-FI/E15236_TUF_GAMING_X570-PLUS_WI-FI_UM_WEB_060319.pdf) states it only has a single M.2 slot that supports PCIe Gen 4 and SATA, but it clearly has two. I am still reading through it though. What sort of info should I look for to determine which slot I should put it in? Again, I haven't purchased anything yet, but I know when I will I want to know what slot I put it in when I build it. 

[Jumballi]

2 minutes ago, Nathanpete said:

The manual (https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/TUF_GAMING_X570-PLUS_WI-FI/E15236_TUF_GAMING_X570-PLUS_WI-FI_UM_WEB_060319.pdf) states it only has a single M.2 slot that supports PCIe Gen 4 and SATA, but it clearly has two. I am still reading through it though. What sort of info should I look for to determine which slot I should put it in? Again, I haven't purchased anything yet, but I know when I will I want to know what slot I put it in when I build it. 

On the manual, it should give names to each port, ie m.2_1 and m.2_2, and it will point out where on the motherboard and which port shares lanes with what.

[iBabySlapper]

See page 1-16 for reference, but for a 3rd gen Ryzen CPU, both M2 slots are Pcie 4/SATA compatible. As far as I can tell, the top x16 slot will always run PCIe 4 x16, but the lower X16 slot can also go down to x4 speeds if the top slot is occupied.

[Nathanpete]

Just now, Jumballi said:

On the manual, it should give names to each port, ie m.2_1 and m.2_2, and it will point out where on the motherboard and which port shares lanes with what.

It does not state which lanes are shared. It does say that the top slot "M.2_1" (w/ 3rd gen Ryzen) has PCIe 4 x4 and SATA support, and for all ryzen processors the M.2_2 slot supports PCIe 4.0 x4 and SATA. That means the bottom slot is connected directly to the chipset right? I don't totally understand what PCIe lanes are or how they work, other than that the CPU only offers so many and that the GPU and SSD want a slice of each. 

[iBabySlapper]

5 minutes ago, Nathanpete said:

It does not state which lanes are shared. It does say that the top slot "M.2_1" (w/ 3rd gen Ryzen) has PCIe 4 x4 and SATA support, and for all ryzen processors the M.2_2 slot supports PCIe 4.0 x4 and SATA. That means the bottom slot is connected directly to the chipset right? I don't totally understand what PCIe lanes are or how they work, other than that the CPU only offers so many and that the GPU and SSD want a slice of each. 

The chipset offers a certain amount of lanes, and so does the CPU, and both are connected to each other. The diagram is a reference for the X570 chipset, and it can differ, but it should make things clearer.

[Nathanpete]

1 minute ago, iBabySlapper said:

See page 1-16 for reference, but for a 3rd gen Ryzen CPU, both M2 slots are Pcie 4/SATA compatible. As far as I can tell, the top x16 slot will always run PCIe 4 x16, but the lower X16 slot can also go down to x4 speeds if the top slot is occupied.

Just found that for myself too by reading it. I will not be using the bottom PCIe x16 slot yet, and probably never will, but it is there for the future. It says something about the bottom M.2 slot and all the SATA ports being connected to the chipset directly, so I don't know what that means for the top M.2 slot. Does the top M.2 slot still have more bandwidth than the bottom one, like in most PCIe situations? Basically, do I use the bottom slot because the GPU needs the bandwidth, or  would I actually see a boost in performance by connecting the 970 Evo to the top slot without the heatsink? 

[iBabySlapper]

1 minute ago, Nathanpete said:

Just found that for myself too by reading it. I will not be using the bottom PCIe x16 slot yet, and probably never will, but it is there for the future. It says something about the bottom M.2 slot and all the SATA ports being connected to the chipset directly, so I don't know what that means for the top M.2 slot. Does the top M.2 slot still have more bandwidth than the bottom one, like in most PCIe situations? Basically, do I use the bottom slot because the GPU needs the bandwidth, or  would I actually see a boost in performance by connecting the 970 Evo to the top slot without the heatsink? 

No, both slots run at the same speed regardless of graphics configuration, so it won't matter where you put the SSD.

[iBabySlapper]

This is completely spectulation, but I believe the bottom slot is connected to the chipset, and the top slot is provided by the CPU. Since the bottom slot is always PCIe 4 regardless of CPU, and the top slot can change in bandwith dependant on CPU. It's probably better to use the top slot in this case, but whether there is actually a noticable difference is another story.

[Nathanpete]

3 minutes ago, iBabySlapper said:

No, both slots run at the same speed regardless of graphics configuration, so it won't matter where you put the SSD.

So does the top x16 slot and the top M.2 slot interface with the CPU lanes, and by using the chipsets lanes I won't be seeing a bandwidth choke? Based on what I just quoted I will just be using the bottom slot because I don't see how the heatsink could harm anything. 

[iBabySlapper]

5 minutes ago, Nathanpete said:

So does the top x16 slot and the top M.2 slot interface with the CPU lanes, and by using the chipsets lanes I won't be seeing a bandwidth choke? Based on what I just quoted I will just be using the bottom slot because I don't see how the heatsink could harm anything. 

Yeah, it depends. If you're pushing more than PCIe 4.0 x4 speeds through the chipset (which I believe is around 7 Gb/s) it may slow down. But that's a lot of conectivity, you're not really that likely to hit that kind of speed unless you have many highspeed USB devices (and the NVME SSD) connected and going full tilt at once. I would personally put the SSD in the top slot anyway.