X99 Motherboard to support SLI and NVMe?

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Crash55

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For my new build I will be using:
Core i7-6850k
2x EVGA GTX 1080 FTW
an NVMe drive - preferred drive is 1.2TB Intel 750, could use Samsung 950

Since the CPU supports 40 lanes I want to have the GPU's at x16 and the drive at x4. I am currently looking at three motherboards and was hoping someone can tell me if the will work or not. After reading the ROG forums I am concerned that I could wind up slowing down the primary graphics slot. I know there is little difference between x16 and x8 but if I am spending this much money I want everything right.

Asus Rampage V Edition 10
The GPUs would go in slots 1 and 3. That leaves slot 4, M.2 and U.2 available.
However I saw on the Asus ROG boards that using slot 4 causes issues and that if you use the U.2 slot it turns on the M.2 and reduces slot 1 to x8.
So it looks like only an M2. drive would work with this board?

EVGA X99 FTW K
The GPUs would go in slots 1 and 5. That leaves slot 6 and M.2 available.
So the Intel 750 would have to go in slot 6 or a Samsung in M.2.
Does anyone have any experience doing this?

MSI X99AGodlike Gaming Carbon
GPUs would go in Slot 1 and 4. That leaves slot 5 and M.2 available
The Intel 750 could go in slot 5 or use the U.2 adapter in the M.2 slot or Samsung 950 in M.2 slot
Does anyone have any experience doing this?



 
Solution
jimmysmitty
As I said I don't see why Asus would say anything and not have it correct. The U.2 and M.2 should only pull from the x4 PCIe slot which would be disabled if the M.2/U.2 is used and the M.2/U.2 should be disabled if the x4 PCIe is being used.
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jimmysmitty

jimmysmitty

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Where are you getting the info for the ROG board?

The PCIE_X8_4 slot shares bandwidth with the M.2 x 4. When PCIE_
X8_4 is occupied, the M.2 will be disabled. The PCIE_X8_4 slot will be
disabled when using a 28-LANE CPU
Click to expand...

That is from the current version of this board and short of a few updates and the RGB this version you listed should be similar. From what I can tell slot 4 is all that would be affected by using the M.2 slot and not PCIe slot 1.
 
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Crash55

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From the ROG forum and a comment on NewEgg. I know the manual says something different but that is what people are seeing. I have an email into their tech support but no reply yet.
 
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Crash55

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In one of the threads they posted a diagram of the chipset and there are dashed lines connecting M.2 / U.2 back to PCIe 3.0 Slot 1. The manual claims that they share bandwidth with PCIe Slot 4.

It appears that the U.2 slot is dependent upon the M.2 so it can't work without that one activated. So when you turn on the U.2 you turn on the M.2 as well and it throws the board into 4 way SLI mode with them activated. That reduces all the PCIe 3.o slots to x8.

What is really bugging me is that using Slot 1, Slot 3 and M.2 and U.2 should account for 40 lanes so no need to reduce the slots to x8. It is almost like you can only actually use 39 lanes so when try to activate 40 it drops the speed down.

I will update the thread if I ever get an official answer. If not I may go with the MSI board instead as its manual explicitly lists the U.2 (adapter in M.2 slot) running at x4 with x16 SLI. Also not getting answer makes me nervous about what other gremlins could be hiding in the Asus board
 
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Crash55

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I found someone running what I plan to - 2x GTX 1080's and an Intel 750 using U.2. He is getting full X16 on both GPU's. So either the person had a bad motherboard or doings something wrong
 
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jimmysmitty

jimmysmitty

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As I said I don't see why Asus would say anything and not have it correct. The U.2 and M.2 should only pull from the x4 PCIe slot which would be disabled if the M.2/U.2 is used and the M.2/U.2 should be disabled if the x4 PCIe is being used.
 
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Solution
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Crash55

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I finally had someone with the same hardware (2x 1080's and Intel 750 on U.2) and everything is running fine. So either the other person had something else wrong or threads for 28 ad 40 lane CPU's were getting mixed up.
 
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Crash55

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The thread started with him having the 6800k which is a 28 lane CPU. He then got a 6850k (40 lane) and that is when he started complaining that using the U.2 turns on the M.2 and reduced his first GPU slot to x8. So I am not sure what was going on. He only had a single video card so even if both U.2 and M.2 were on he would only be using 24 lanes.

The issues with slot 4 messing with slot 1 was another thread.
 
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Crash55

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I don't know what happened. I do know that with a 28 lane CPU running the M.2 and U.2 slots with a single video card reduced the card to x8, even though it shouldn't have since he was using only 24 lanes. Asus replied to his review stating this at NewEgg and there answer was to get a 40 lane CPU - not a reassuring answer
 
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Crash55

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So new confusing information. A week ago I asked this question to ASUS tech support and this is the answer I just received today:

Dear Andrew,

Thank you for contacting ASUS Technical Support.

We are writing back to you regarding the issue with the board.

I checked and found that it is a motherboard design limitation, So two GPU, it will drop to x8 with U.2. You can use hyperkit or M.2 with 950 Pro to acheive 16x for 2 GPU.

For any further queries, please feel free to reply to this E-Mail. We will be glad to assist you.

Thank you for choosing ASUS.

Regards,
Arnold. K
 
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