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Ryzen 9 3950X will i have enough lanes?

Hello, All!

Essentially I am deciding between getting Ryzen 9 3950X and the Threadripper 2950X. Although i have read a lot of content online I am a little fuzzy on the details in terms of ulizing PCIe lanes.

I want to run two 1080s in SLI and two NVME in Raid-0 for Linux and another SSD for windows. I would like to use all this hardware at its full capacity.

My thoughts is that this will work because a total of 16x lanes will be used for SLI (8x each) and 8x lanes for the raid configuration (4x each). For a total of 24 PCIe lanes which AMD’s X570 should be at it’s limit.

(0) Is it possible to run SLI at 16x/16x? And an argument for going threadripper?
(1) is this reasoning correct?
(2) What happens if I put another m.2 ssd in the X570 configuration? Will I be able to use it as a SATA (for my windows install) while using the two NVMEs in raid?
(3) Any other build tips would be recommended?

As far as I know, you can’t run the GPUs at x16 in SLI on X570. I have seen some testing done on this before and the difference with x8 was negligible in most cases, at least with the 1080: https://www.techpowerup.com/review/nvidia-geforce-gtx-1080-pci-express-scaling/

It might be more of an issue with more powerful cards like the 2080 Ti. I’m not sure if it is an argument for going Threadripper though - the 2950X already bottlenecks a 2080 Ti in some games at higher refresh rates. Personally, I’d go with the 3950X especially if you plan on upgrading the GPUs later.

Doesn’t X570 have PCI-e 4.0 also? I don’t think current cards take advantage of that, but presumably, future ones will be able to use the additional bandwidth - so x8 may not be as limiting in that case.

yes, you can run sli in a by16 by16 config. just not on AM4 based Ryzen system. It is also expected to stay that way because of segmentation.

if you were to really need those lanes, threadripper would be the choice.
BUT you are also pitting a not jet avaialbe CPU against a Zen+ chip which is bonkers. IF you can wait for the 3950x, you can wait for the equivalent Threadripper.

On the technical side of X570, you could squeeze two pcie 3.0 by nvme ssds through the By4 4.0 interface of the chipset and still use the extra by4 4.0 lanes from the cpu.

In a scenario where you have one ssd on the cpu and one on the chipset, you will probably enter voodoo and BS hell of issues when trying to raid them.

have a look at the platform docs, should tell you plenty what could work and what couldn’t .

  1. nope, as the AM4 Socket only has 24 lanes possible - 4 for the CHipset, so only 20 are usable. Old Zen1(+) CPUs had 32 Lanes so it would have been possible - without any other PCIe devices, without Chipset. But also limited by the AM4 Package.
    1)hm, not really. But you need a really expensive X570 Board in the 300€ Range as the “cheaper”, ~250€ or less ones don’t have the necessary Switchers to switch from 16 to 8/8
  2. your bandwith is limited by the Interface from CPU to Chipset. In general, 2 m.2 SSD should be fine on the X570 Chipset. A 3rd one connected to the Chipset means that you can use only 2 at the max. Bandwith, the 3rd one might be “clipped”.
  3. yeah, wait for Zen2 based Threadripper coming later this year. Isn’t September rumored for the release of the 3000 series Threadripper?

TL;DR:
Looks like its more something for the Threadrippers, though it also is possible for the AM4 Plattform.

The easiest solution would be to get rid of the 2 GPUs and replace it with a modern, better one, as SLI hardly works with any modern (modern = released in 2018 or later) game anyway…

Totally agree for games but i also do data science and play around with deep learning libraries. This gives me a lot to consider.

Yeah, but the Turing has improved Async Compute for example. Might want to take a look at the performance.

If they didn’t cripple the GPU with the Driver, wich is highly likely, it should be a good amount faster than two old Pascal Cards…

Why?

Just buy a 1080ti for less money and get better, more consistent performance. SLI and Crossfire is dead. Most games do not support it in 2019 - and the older stuff that works with SLI/crossfire reliably will run just fine on weaker cards than a single 1070-1080 anyway.

My advice would be “don’t build a machine for SLI”. If that is the only potential need you have for PCIe lanes, fear not - just buy a decent single graphics card - you have enough lanes for that.

If you still think you need PCIe lanes, or you want to ignore the above advice and reckon you have a use for SLI anyway, and want to ensure x16/x16 - you need threadripper.

That’s not SLI (2 gpus is not automatically SLI), that’s just multi-gpu. And likely doesn’t need faster than x8… but YMMV - check your workload.

Perhaps you know all this already, just to remind, running linux from raid devices needs some tinkering to get set up and working. For example the choice of bootloader etc.

Remember, you are hardly accessing the windows device while you are running in linux and vice versa. So having all 3 nvme’s able to run 100% same time hardly a thing, and if copying from one to another, the raid devices will only do half the work.

I don’t have anything to add about the gpu’s.

I think, i would just go with 3950x, if it’s enough good for the use i had for it.

Waiting for reviews is usually advised.