• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Installing an RTX 3080 in a second PCIe slot: Does it affect the performance?

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

backintime

Registered
Joined
Sep 30, 2020
Hi everyone,

CPU: AMD Ryzen 9 5950X
MOBO: ASUS ROG Crosshair VIII Dark Hero

I'm trying to figure out a way to install four M.2 NVMe modules on my new ASUS Dark Hero motherboard, which has only two M.2 slots.

The ASUS HYPER M.2 X16 GEN 4 CARD seems like great solution to add four extra modules, however, the only way for four modules to work on this card, is to use the first PCIe slot. I never heard about this, but this seems related to Bifurcation and being able to run two or four modules, depending on which slot I'd use. Slot two only allows me to use 2 modules.

So basically, if I want to continue with this GEN 4 card, I have to install my future RTX 3080 card in the second PCIe slot. Which, according to the manual (click here) on page 1-8, should be x16 as well? Or do those dashes mean that it's not x16?

I was hoping if anyone could tell me if I'd lose any GPU performance from using the second slot.

Thank you! 😁
 

Ben333

Folding for Team 32!
Joined
Feb 18, 2007
AMD Ryzen™ 5000 and 3000 Series Desktop Processors - 2 x PCIe 4.0 x16 SafeSlots (support x16, x8/x8)
AMD Ryzen™ 4000 G-Series and 2000 series Desktop Processors - 2 x PCIe 3.0 x16 SafeSlots (support x16, x8/x8)
AMD Ryzen™ 3000 and 2000 G-Series Desktop Processors - 1 x PCIe 3.0 x16 SafeSlot (supports x8)
AMD X570 chipset - 1 x PCIe 4.0 x16 (supports x4) - 1 x PCIe 4.0 x1

manpage.png

Pretty sure only your top-most slot is full 16x.

Would running the card at 8x bottle neck you? I have heard that you would lose only a very small amount of performance. But personally, I'd keep it in the top slot.

The ASUS HYPER M.2 X16 GEN 4 CARD seems like great solution to add four extra modules, however, the only way for four modules to work on this card, is to use the first PCIe slot. I never heard about this, but this seems related to Bifurcation and being able to run two or four modules, depending on which slot I'd use. Slot two only allows me to use 2 modules.

^ Seems you kinda answered your own question.

You may find this useful, here is a link to a discussion over at hardforum on the topic of running a 3080 in an 8x slot https://hardforum.com/threads/rtx-3080-on-pci-e-3-0-x16-vs-x8.2001596/
 
Last edited:
OP
B

backintime

Registered
Joined
Sep 30, 2020
Thank you for your answer!

I will definitely look around on this board to see if I can find more answers regarding alternatives for the ASUS GEN 4 card. I had hoped those dashes (stripes) meant a repetition of the number above, but I figured I might be wrong 😁

Thanks!
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
The top slot is always (more than typically - I can't think of a situation where it isn't) the primary GPU slot and gets x16 lanes from the CPU. When something is populating the second PCIe slot, both the Primary and second slot goes to x8. The third slot is sourced from the chipset and is uneffected.

I'd get a PCIe card with 2 M.2 sockets and use the second slot (first still goes to x8). This way you can use the two on the board and two from the card. Anyway you slice it, you'll split the GPU lanes to x8/x8 when using either PCIe slot. Top or bottom doesn't matter.

I have to ask... why 4x M.2 storage modules? You can't run two and two SATA based 2.5" SSDs? What kind of bandwidth do you need? Can you run it on the 3rd PCIe slot (2 M.2 ssds).. do all your drives need to be banging fast PCIe 4.0... or will 2x 3.0 x4's do ok?

As far as performance losses from running a 3080 in a x8 PCIe slot, negligible really...
https://www.techpowerup.com/review/nvidia-geforce-rtx-3080-pci-express-scaling/27.html
 
Last edited:
OP
B

backintime

Registered
Joined
Sep 30, 2020
Hi, thank you for your message!

Why not get a card with two M.2 sockets on it and use the second slot...?

That is exactly what I'm going to do. I was thinking about maybe running the ASUS GEN 4 card in slot two (which basically let's it run two anyway), but I'm going to see if there are any good alternatives without a fan (headsink or something). In terms of keeping the case as quiet as possible (hence one of the choices to go with the ASUS Dark Hero).

Like you mentioned, it's not really worth to cut on GPU performance.

I have to ask... why 4x M.2 storage modules? You can't run two and two SATA based 2.5" SSDs?

I'm coming from an older MSI X399 motherboard which had three M.2 slots. I bought 1000/500/500 960 EVO's back than. For my upgrade, I bought a 980 1TB Pro and a WD GOLD 14TB SATA drive. I think it's a waste of 'speed' (and space) to not use the older M.2 modules. That's basically my only reason for running four of them. I should probably mention this is a video editing workstation 😁 In terms of using (at least) the ADOBE suite, it's very profitable to have separate drives at high speeds like that.
 

Ben333

Folding for Team 32!
Joined
Feb 18, 2007
Well, you wouldn't take much of a hit at all on GPU performance. If doing work is this computers primary role then yeah I'd keep all your M.2 drives for sure. EarthDog made a good point, if using both slots makes the top reduce to 8x anyway then I guess it doesn't matter where the GPU is. Of course, that said, your top slot would no longer be running full 16x so you couldn't use all 4 m.2s in there. (This is how I'm understanding it anyway)
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
Like you mentioned, it's not really worth to cut on GPU performance.
I didn't mention such a thing. There are negligible losses (read my link). ;)

As far as your need...just want to make sure it wasn't some wonky config in your head. You're good. :)



But yeah, use the two that are integrated, then use the other two on an add-in-card (AIC).

You could likely put your fastest drives (PCIe 4.0 x4 models) on the integrated sockets and the slower ones on the add-in-card in the third slot. So long as they are PCIe 3.0 x4 drives, they will get the full bandwidth from the 3rd s.ot/PCIe 4.0 x4 slot.

Of course, that said, your top slot would no longer be running full 16x so you couldn't use all 4 m.2s in there. (This is how I'm understanding it anyway)
If he wanted PCIe 4.0 x4 for 4 drives, he would need to plug the AIC into the top/primary socket and nothing else installed in the second slot. Then he would need to move his GPU to the 3rd slot which runs at PCIe 4.0 x4. There you will lose a few % performance according to my link from earlier.
 
Last edited:
OP
B

backintime

Registered
Joined
Sep 30, 2020
@Ben 333: Thank you for your comment. I must be mixing things up now, but do you mean that if the GPU would be installed in PCIe slot 2, and the four M.2 modules on a card in PCIe slot 1, slot 1 wouldn't be able to reach x4 x4 x4 x4 because the GPU would take away any speed? I mean... this won't apply to me no more, but just curious what you meant with your last line 😁

@EarthDog: Thanks again! I thought I gave a quick 'summarize' by using the word 'cut' 😉

I'm no where near 'good'. The last time I was still active in IT was back in 2006, lol. Since then my knowledge basically has been brought down to media/television/film 😁

All older M.2 modules are PCIe 3.0 x4. I think I'll install the newer 980 1TB Pro + older 960 EVO 1TB on the board and use an alternative PCIe 3.0 or 4.0 M.2 card.

Thanks again! 😁
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
@Ben 333: Thank you for your comment. I must be mixing things up now, but do you mean that if the GPU would be installed in PCIe slot 2, and the four M.2 modules on a card in PCIe slot 1, slot 1 wouldn't be able to reach x4 x4 x4 x4 because the GPU would take away any speed?
Correct. It's not so much the GPU taking it as any device plugged in the second slot causes BOTH slots to run x8/x8. Those slots are given its bandwidth by the CPU which has 16 lanes total. So anytime anything is plugged into the second slot, the first slot drops to x8.
 

Ben333

Folding for Team 32!
Joined
Feb 18, 2007
When you use the 2nd PCIE 16 slot, BOTH slots 1 & 2 will only run at 8x. So as EarthDog said, in order to get 16x full to any device, the 2nd slot must be empty.

EDIT: He beat me to it. :)
 
OP
B

backintime

Registered
Joined
Sep 30, 2020
Correct. It's not so much the GPU taking it as any device plugged in the second slot causes BOTH slots to run x8/x8. Those slots are given its bandwidth by the CPU which has 16 lanes total. So anytime anything is plugged into the second slot, the first slot drops to x8.

Thanks for both your answers. I never knew about that. Good to know. This will help me a lot in my search for an alternative M.2 card.

Thanks! 😁
 

dfonda

Senior Golfer
Joined
Feb 25, 2004
backintime...if you go forward in time , by the time you can actually get an RTX 3080 ...M.2 8TB drives will only cost $100...and you'll only need 2...:chair::D

Plus the RTX 4080 might be released...:p
 
OP
B

backintime

Registered
Joined
Sep 30, 2020
Haha. Unlike everyone else, the only thing I'm waiting for is the RTX 3080 20GB card. Got a 1080 ti which runs at 11GB. I'm not in that much hurry that I needed a normal 3080/3090. The new RDNA cards aren't the best in terms of CUDA cores being better than Compute Units.

But yeah, it would certainly make a difference if we could skip a few months ;)
 

Mozhand

New Member
Joined
May 17, 2021
What happens if you just plug a graphics card in the second slot is it still 16?

What happens if you just plug a graphics card in the second slot is it still 16?