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Samsung 950 Pro M.2 in an ASUS X99-Deluxe II w/ and i7-5820K and 2 GPUs in x16x8 Crossfire

Hi,

I am gathering parts for a new build and am about to purchase an ASUS X99-Deluxe II. I already have settled on an i7-5820K and am aware that it is limited to 28 PCIe lanes. Since buying the CPU, I have become very interested in getting a Samsung 905 Pro M.2 drive. I am looking at the manual for the X99-Deluxe II and see that if I use 2 GPUs, they will be limited to x16x8. I am OK with that.

The manual shows that for a 40-lane CPU, the M.2 and U.2-1 ports share BW with PCIEX16-3 and U.2-2 shares BW with PCIEX16-5. In the 28-lane CPU diagram, the M.2 and U.2 headers are not mentioned at all. I see that the MOBO comes with an onboard M.2x4 bracket and a Hyper M2.x4 Mini card to mount in a PCIe slot. My question is with the 28-lane i7-5820K, can I achieve a setup on the X99-Deluxe II MOBO that will give me 4 full lanes for the Samsung 950 Pro, while using 2 GPUs in Crossfire? If not, can I get 4 full lanes for the 950 Pro if I just have 1 GPU? The GPUs are ASUS R9-380s.

If this can be done (with 2 or 1 GPU), can I use the onboard M.2 bracket and header or do I have to use the Hyper M.2x4 Mini Card or does it not matter? Is it possible at all, and if so, what PCIe slots do I plug in the GPUs and the Hyper M.2x4 card (if that is what I have to use to do it).

I read some similar threads here that say you can do it, but not for this particular MOBO. It may be a limitation of how the MOBO shares PCIe bandwidth. It worries me because in the X99-Deluxe II manual, the PCIe lane allocation diagram for a 28-lane CPU does not even show or list the M.2 header or either U.2 header.

Kind of wishing I had sprung for a 40-lane CPU but I was not considering a 4-lane M.2 drive when I bought the i7-5820K, plus I got it for a really great price.

Thanks in advance for any responses.
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  1. Best answer
    In section 1.1.5 the manual addresses the expansion slots (pg 1-(7-10)). First we see that for dual GPUs you are suggested to install them in x16/x8 mode in slots 1 and 3. This clearly consumes 24 lanes of the 28 available. For a 40 lane CPU one would use slots 1 and 3 as well but it would operate in x16/x16 mode using 32 of the 40 lanes.

    On page 1-9 and 1-10 it address how the SATA Express, U2, and M2 sockets work with the various PCIe slots. Here we see for a 28 lane CPU there is no mention of the M2 socket, but for a 40 lane CPU it is very clear that the M2 socket is shared with PCIe slot 3. In this case, for a 40 lane CPU, the GPUs would operate in x16/x8 mode and the M.2 socket takes 4 PCIe lanes from slot 3. It would seem to me that what happens with a 28 lane CPU is that the M2 slot is disabled when PCIe slot 3 is used. Thus instead of dropping to x8/x8 mode and siphoning 8 lanes from slot 1 to supply the M2 socket, it instead refuses to operate in x16/x4 mode which would enable 4 lanes from slot 3 to be used by the M2 socket. The manual suggests looking at page 1-30 for more information about the M.2 socket, however this page offers no actual help.

    Now, the upside. Look back at page 1-8: consider a triple GPU setup. It can offer x8/x8/x8 mode on a 28 lane CPU using slots 1, 3, and 4. What this means is that you'll need to use the Hyper M.2 converter card to install a Samsung 950 Pro as a PCIe card rather than using the native M.2 socket, but if you do this you can install it in slot 4 and have it run in x4 mode along with both GPUs in x8 mode. This should yield an x8/x8/x4 configuration, though you're clearly losing some lanes here. Slots 2 and 5 would operate in PCIe 2.0 mode only on a 28 lane CPU but if all you really need is the dual GPUs and the NVMe SSD plus some SATA devices and maybe some PCIe 2.0 cards, this is a pretty good solution though it's a bit sad that neither U.2 port nor the M.2 socket would be available.

    Thing is that manuals say "GPU" when they really just mean any PCIe card. My system for example uses a PCIe 2.0 x8 RAID controller which I'm able to operate at full speed because the motherboard supports SLI. I only have one GPU, but because there are two x8 or x16 cards installed it drops to x8/x8 mode rather than x16/x0. The same should happen here - you put the Hyper M.2 card in the 4th slot and the system thinks it's in a 3-way setup and runs at x8/x8/x4. You probably lose the 4 lanes that would go to the 4th slot in a true 3-way GPU setup (x8/x8/x8) but aside from that, it *should* run.

    I'd suggest looking up some reviews as this board is brand new and see if they specifically mention the ability to use M.2 on a 28 lane CPU or not.
  2. Thank you for your detailed response. I am staring at the manual for the X99-Deluxe II and I agree with what you are suggesting about putting the 2 GPUs in slots 1 and 3, and the M.2 Hyper Card in slot 4 to end up with 8x8x4. I also agree I am going to have to scour the web for posts from people who have a 28-lane CPU and this card and have done (or tried to do) what I am hoping to do. I do have a few questions.

    1 - I see on page 1-7 is says slot 1 is "PCIe 3.0/2.0 x16_1 slot" and slot 3 is PCIe 2.0 x16_2 slot". I will profess my ignorance and ask what does the _1 slot and _2 slot mean? Are they just numbering the x16 slots? It also says slot 4 is "PCIe 3.0/2.0 x16_3 slot" so wouldn't it be better to put the 2 GPUs in slots 1 & 4 rather than 1 & 3? Slot 3 is listed as PCIE2.0x16 - not 3.0x16. I see on page 1-8 that it clearly says in a dual card setup to use slots 1 and 3. I just don't understand why it says on page 1-7 that slot 3 is PCIe 2.0 only.

    2 - I also see on page 1-8 where is says in a 3 card setup to use slots 1, 3, and 4 so I agree that I should be able to put the GPUs in slots 1 & 3 and the M.2 Hyper Card in slot 4 and end up with the GPUs running at x8x8 and the M.2 at x4 (hopefully). That adds up to 20 of the 28 lanes. I don't understand why I have to lose 8 lanes. Why can't I put the 2 GPUs in slots 1 & 4 (that both say PCIe 3.0/2.0 x 16) and put the Hyper Card in slot 5 or 6? It seems from the charts on page 1-8 that no scenario adds up to the full 28 lanes. Are the last 4 or 8 lanes reserved for PCIe 2.0 stuff?

    3 - This particular MOBO has an additonal PCIe x16 slot - 4 verses 3 for the X99-E, X99-A II, and ROG Strix X99 gaming. Does this extra slot do me any good, considering I am limited by a 28-lane CPU or is there no point in me buying a MOBO that has the extra PCIe 3.0 slot?

    I admit to getting confused about the PCIe slot terminology and how the MOBO allocates lanes. It seems like if the CPU has 28 lanes, I should be able to "get at" all of them. Thanks so much for your help, and anyone else who wants to chime in an educate me.
  3. Thinking about this some more, I think you (and the manual) mean to do a 3-way setup, to use PHYSICAL slots 1, 4 and 5 which are all called out as PCIe 3.0/2.0x16. This is because physical slot 3 is PCIE 2.0x16. I found a post on New Egg from a guy complaining about the fact that on the X99-Deluxe II, physical slot 3 was "downgraded" to PCIe 2.0 relative to the older X-99 Deluxe and X99-Deluxe/U3.1. His complaint was that this forced him to have to use physical slots 1, 4, & 5 for the 3 GPUs and putting a large GPU in physical slot 5 totally blocks the headers for case front I/O (USB, audio, power switch, & LED). So I think I understand now that you and the manual are referring to PCIe 3.0x16 slots 1, 3, & 4 which are PHYSICAL slots 1, 4 and 5. Is this correct?

    My other questions in the post above remain. Sorry if I am giving anyone a headache !!
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