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Thread: PCI-E Lanes, M.2 drives andl x299 motherboards = confusion

  1. #1
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    PCI-E Lanes, M.2 drives andl x299 motherboards = confusion

    Hi guys

    I shall be either building or buying an x299 Intel Skylake system soon and I've hit a wall in trying to comprehend the issue of Lanes. The system will be something similar to this:

    Intel Core i9-7900X 10 Core Skylake - 44 lanes OR i7-7820X 8 Core Skylake - 28 lanes
    ASUS ROG Rampage VI Extreme motherboard OR ASUS ROG Rampage VI Apex (I'm open to other suggestions)
    32GB Corsair Vengeance RGB Pro 3000Mhz RAM
    I already have an nVidia GTX 1080Ti and I will not go down the SLI route
    I already have x2 M.2 drives and 3 regular SSDs
    Phanteks Evolv X

    However, it's possible I will get another M.2 drive so I'll have 3 in total but I don't know where that will leave me with regard to Lanes or whether I shouldn't worry about it or what. If you can help or point me in the direction of a good online article that would be much appreciated.

    Any comments or views would be VERY welcome! Thank you.

  2. #2
    Xtreme Owner Charles Wirth's Avatar
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    PCH is 4 lanes only and shares with other devices like USB, network, and sound. The PCH controls the 6G SATA ports.

    Apex or Extreme you have use of all pcie slots, you can use the Dimm.2 card that comes with asus mobo to connect 2x m.2 to the PCH or the CPU, I highly suggest the CPU (connection closest to back panel)

    Go into bios and set last PCIe slot to DIMM.2 and reboot, you should be able to boot to M.2 if you had OS on it.

    M.2 are usually 4x pcie lanes so you don't want more than 1 on the PCH

    You can but VROC card ($89) and that supports 4x M.2 and uses 4x lanes for each M.2 added. This would give you a total of 6x M.2 slots.

    If you are using Intel SSD's you can RAID DIMM.2 and the VROC (span) together, other drives no.

    Now to CPU selection, the 28 lanes will disable 1 PCIE slot, check mfg website for CPU handling of PCIE slots, I cant remember because I only have 44 lanes.
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  3. #3
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    Hi Charles

    Very many thanks for the reply - it's much appreciated and sorry for not responding sooner.

    So, just to be sure I've understood this correctly and going with the premise that I'll have x3 m.2 drives:

    If I were to get the Apex board it includes two ROG DIMM.2 modules that supports a total of four PCIe 3.0 x4 M.2 SSDs (there are two DIMM.2 expansion slots on the board).

    I would connect x2 m.2 cards to one of the DIMM.2 cards and insert it into the slot that's nearest the in/out plate as you say as this is the CPU one.

    The 3rd m.2 drive would need to be connected to a PCIe slot via something like the VROC card you suggested and then I'd need to tweak with the BIOS to set this slot to DIMM.2 also.

    I'll have then used up x12 lanes for the m.2 drives and 16 lanes for the GPU so 28 lanes should be OK for me...unless I decide to use even more m.2 drives! Is this correct?

    Thanks again.

  4. #4
    Xtreme Owner Charles Wirth's Avatar
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    Rampage Apex has 2x DIMM.2 slots, and yes the one near the IO plate is connected to the CPU.

    If one of your drives is just a data drive then connecting it through the PCH should be fine.

    You can get a cheap PCIE to M.2 card for the third M.2 if you wish to connect that through the CPU.

    The Apex has 4x PCIE slots with shroud, they look like 16x slots but only two are, slots 0 and 2 are 16x. These are all configurable for bifurcation (CPU RAID use) in BIOS and this includes the CPU DIMM.2 slot.

    There is a non shrouded 4x pcie slot, not sure where that connects but iirc it doesn't have stub in bios to control its usages as a drive slot.
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  5. #5
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    I think I'll get a PCIe to M.2 card for the 3rd drive but I presume it'll only ever use 4 lanes regardless of whether it's connected through the PCH or via a PCIe slot.

    Thank you for taking the time to help with this.

  6. #6
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    Thanks, Charles, that was helpful.
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