[SOLVED] Ausu Z790-e shares bandwith with GPU and M.2 drives? How can I get max performance?

[Spitfire7]

So I just got the new ASUS Z790-e and a new Internal SSD M.2 drive. I hear from ASUS that the 1st M.2 slot shares the bandwitch with the PCIe for the graphics card, meaning it slows the PCIe from 16x read speed down to 8x. How can I get around this? Is it as simple as installing the M.2 SSD in the 2nd M.2 slot?

Why did they do this? This sounds like a major flaw. I would want to use the #1 M.2 slot with the cool extra advanced cooling heatsink, but now I can't since that will slow down my graphics card performance. This is really stupid. Am I missing something here?

 

[bill001g]

That is what it appears they did but I am no expert on pcie lanes.

The obvious reason they did it was the cpu only has 16 pcie5 lanes and if you want a m.2 device than can also run pcie5 then you have to split them between the video card slot and the m.2.
Maybe we might see a m.2 pcie5 drive but even the newest video cards that were just released can't use pcie5. If a current video card existed that could use pcie5 then it could run with just 8 lanes

What would be bad is if it also requires you to split the lanes even if you are using pcie4, which I suspect it does.

Other than not being able to use the fancy heat sink I can't see much downside. You just have to find the other m.2 slot that runs the 4 pcie4 lanes that come off the cpu.

I suspect by the time we get video cards that can fully use pcie-5 x16 and m.2 pcie-5 devices are common we will have new cpu and motherboard that can resolve this issue.

 

[kanewolf]

So I just got the new ASUS Z790-e and a new Internal SSD M.2 drive. I hear from ASUS that the 1st M.2 slot shares the bandwitch with the PCIe for the graphics card, meaning it slows the PCIe from 16x read speed down to 8x. How can I get around this? Is it as simple as installing the M.2 SSD in the 2nd M.2 slot?

Why did they do this? This sounds like a major flaw. I would want to use the #1 M.2 slot with the cool extra advanced cooling heatsink, but now I can't since that will slow down my graphics card performance. This is really stupid. Am I missing something here?

Then use M.2_2 or M.2_3 those slots will use PCIe lanes from the motherboard chipset.

 

[Spitfire7]

That is what it appears they did but I am no expert on pcie lanes.

The obvious reason they did it was the cpu only has 16 pcie5 lanes and if you want a m.2 device than can also run pcie5 then you have to split them between the video card slot and the m.2.
Maybe we might see a m.2 pcie5 drive but even the newest video cards that were just released can't use pcie5. If a current video card existed that could use pcie5 then it could run with just 8 lanes

What would be bad is if it also requires you to split the lanes even if you are using pcie4, which I suspect it does.

Other than not being able to use the fancy heat sink I can't see much downside. You just have to find the other m.2 slot that runs the 4 pcie4 lanes that come off the cpu.

I suspect by the time we get video cards that can fully use pcie-5 x16 and m.2 pcie-5 devices are common we will have new cpu and motherboard that can resolve this issue.

Okay so I just need to hook my M. 2 drive into M. 2 #2 and both graphics card and m. 2 drive will both be at full max potential speeds? If that's so, easy enough.

The mobo is still in the mail, so I can't see it right now, but are the M. 2 slots easily readable and marked?

 

[bill001g]

Asus is one of the better manufactures of motherboards....you pay a huge premium for them.

I am sure the online manual will tell you all you want to know.

From watch a youtube overclocker called der8auer it seems 4090 do not actually need more than 8 lanes of pcie4 anyway. He had a broken 4090 that only would run 8 lanes and tried unsuccessfully to fix it.

 

[Spitfire7]

Then use M.2_2 or M.2_3 those slots will use PCIe lanes from the motherboard chipset.

Am I at all losing performance or the Samsung 980 Pro's full potential by using the M.2 slot #2?

 

[bill001g]

Yes it will be fine because it is pcie 4 x4 from the cpu not the chipset.

What can be confusing is it is slot m2.2 but if you look at the diagram it is what they call slot-e. It would not be what I would expect to be the second m.2 slot.

After wondering why this does not affect people since most people will just put under the big heat sink it seems running a video card in pcie 4x8 does not hurt performance much even on top end cards very much. Most people would not be able to detect it.

 

[kanewolf]

Am I at all losing performance or the Samsung 980 Pro's full potential by using the M.2 slot #2?

Might you get slightly lower benchmarks?? Yes. Will you see any practical impact?? No.

 

[Spitfire7]

Yes it will be fine because it is pcie 4 x4 from the cpu not the chipset.

What can be confusing is it is slot m2.2 but if you look at the diagram it is what they call slot-e. It would not be what I would expect to be the second m.2 slot.

After wondering why this does not affect people since most people will just put under the big heat sink it seems running a video card in pcie 4x8 does not hurt performance much even on top end cards very much. Most people would not be able to detect it.

That's really helpful and good to know. So for peace of mind I can put the hard drive in slot 2,but probably won't notice any increase.

However, if I want to use the cool heatsink on the board, I can put the hard drive in slot 1, but on paper I might be getting shared slower marks, but won't actually notice it in games.

After consideration, I will probably still install it in slot 2 just because it's nice to know I'm getting all I paid for. Thank you.

 

[Spitfire7]

Asus is one of the better manufactures of motherboards....you pay a huge premium for them.

I am sure the online manual will tell you all you want to know.

From watch a youtube overclocker called der8auer it seems 4090 do not actually need more than 8 lanes of pcie4 anyway. He had a broken 4090 that only would run 8 lanes and tried unsuccessfully to fix it.

Wait so my RTX3070 ony uses 8x bandwith not 16x? You said 8 lanes so maybe I am getting that confused since using both GPU and M.2 drive in slots one splits the 16x into both now only use 8x bandwitch. Is that what you meant, our modern GPUS only use 8x bandwidth?

 

[bill001g]

That is the downside ? of using that first slot. It splits the 16 lanes into 2 8 lane connections.

8 lanes of pcie4 is still almost 16gbytes/sec which is more than even a 4090 needs.

There is a total of 32GBYTES of bandwidth it is just split between the 2 ports. Now if you could run pcie5 it would split 64gbytes of bandwidth.

I assume there is some advantage to not splitting it but it is not something you are going to be able to really tell.

If you are concerned just use the m.2 #2 slot. It has 4 dedicated pcie lanes from the cpu chip.

If you look about 1/2 way down this link you will find the table that shows the bandwidth vs pcie type and number of lanes.


https://en.wikipedia.org/wiki/PCI_Express

 

[Spitfire7]

That is the downside ? of using that first slot. It splits the 16 lanes into 2 8 lane connections.

8 lanes of pcie4 is still almost 16gbytes/sec which is more than even a 4090 needs.

There is a total of 32GBYTES of bandwidth it is just split between the 2 ports. Now if you could run pcie5 it would split 64gbytes of bandwidth.

I assume there is some advantage to not splitting it but it is not something you are going to be able to really tell.

If you are concerned just use the m.2 #2 slot. It has 4 dedicated pcie lanes from the cpu chip.

If you look about 1/2 way down this link you will find the table that shows the bandwidth vs pcie type and number of lanes.


https://en.wikipedia.org/wiki/PCI_Express

Great answer man.

So how much bandwidth is my RTX 3070 using at its full potential?

 

[bill001g]

I have not seen much on that. There are a number of videos and benchmarks on this topic talking about does it matter
what gen of pcie you use to test. They were testing pcie3 vs pcie4 back when there were 3080.

Everything they test though tests number of frames per second which I guess is what is actually important since just getting the data to the memory buffer is only part of the equation.
It seems the delays is always what the card must do to the data between the pcie data buffer and the final output it sends to the monitor.

I kinda don't watch these video much any more because they are boring because they show nothing. You get very tiny difference but it comes down to can a person really see 1 or 2 frames per second that is due to this compare to number of frame variation that happen in games naturally.

I suspect if you were to test say running the card on 1 lane vs 16 you would see some difference but I have never bothered to see if someone tested that.

From what I can tell the first thing we are going to see that can use pcie5 is going to be m.2 ssd. But I don't think they actually increased the speed of the flash chips so it is purely another version of some kind of ram drive sitting in front of your storage.