PCIe Lanes question for ryzen.

Discussion in 'SSD and HDD storage' started by IceVip, Mar 23, 2020.

  1. IceVip

    IceVip Master Guru

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    GPU:
    GTX 1080 Ti @ 2050
    Got an r7 1700 inside a C6H and a 960 evo nvme.

    Question is, since the cpu has 20 lanes, 16 for the gpu (I've only one) and 4 for the nvme, what would
    happen if i take a pci-e x4 to m.2 nvme adapter and stick a Crucial P1 nvme into the last pci-e x16 slot with the adapter?

    Would the gpu drop to x8 or the internal m.2 slot to x2.. any idea?
     
  2. AsiJu

    AsiJu Ancient Guru

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    Not sure but I'd guess GPU drops to x8 because that configuration is essentially the same as SLI / CrossFire.

    Doesn't the mobo manual describe this? Ie. what slot and rate combinations are possible.
     
  3. HARDRESET

    HARDRESET Master Guru

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    My system shows x8 at 3.0 with Asus x470 prime .
    [​IMG]
     
  4. IceVip

    IceVip Master Guru

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    are you running some nvme off of another pcie slot?
     

  5. jbmcmillan

    jbmcmillan Ancient Guru

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    Doesn't it show 8x unless you're stressing the card?
     
  6. HARDRESET

    HARDRESET Master Guru

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    No nvme pcie slot, or m.2
     
  7. The Goose

    The Goose Ancient Guru

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    Hi, im pretty sure it will drop to 8, also if you have sata ports being used they are also sharing resources, but even at 8 you`ll not see much of a drop in performance
     
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  8. IceVip

    IceVip Master Guru

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    Not necessarily. Mine shows x16 without anything running in the background.

    I've read over the years and heard that x8 doesn't do much to the performance. Though i only do 4k in games and i don't know if that means anything to the bandwidth. Thanks for the answer tho, much luv.
     
  9. Astyanax

    Astyanax Ancient Guru

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    It would actually just run off the chipset instead.

    the lanes on ryzen boards are switching type but the bios routes them explicitly
     
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  10. The Goose

    The Goose Ancient Guru

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    Always good to to know.
     

  11. 386SX

    386SX Master Guru

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    GPU:
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    Ryzen has 24 lanes. 16 for gpu, split on PCIEx16_1 and _2 (the first 2 counted from the top downwards).
    PCIEx16_3 is bound to the "southbridge" which is connected to 4 lanes of the CPU.
    Your M.2 slot is connected to the CPU.
    24 lanes summed up.

    Putting the ssd in _3 will clock it at PCIe 2.0 x4 "at best", because depending on sata drives and other factors it will probably clock down to PCIe 2.0 x2 (!!!).
    I own some Intel 750 SSD sticking there and encountered this.

    Asked ASUS support and got told "I plan to use this platform for stuff it isn't designed for". :D

    Feel free to try, but don't expect wonders. ;)

    EDIT: I own an ASUS Strix X370-F. Just FYI.

    EDIT2: I ended up putting the card in _1 (the top slot) and my gpu to _2 (2nd slot), leaving _3 empty. Gpu is split to 3.0 x8 and the drive runs at its intended x4. 4 lanes "wasted", but best performance. No drop in gpu performance notable (Vega64).
    Btw.: There are cards for PCIe 3.0 x8 if you like to go this route and use all x8 lanes.

    https://skinflint.co.uk/supermicro-aoc-slg3-2m2-o-a1711691.html
     
    Last edited: Apr 18, 2020
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  12. pattakosn

    pattakosn New Member

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    I am sorry for slightly hi jacking this post but this is sth I have been looking into lately without much success. Does pcie bifurcation work on all x470/x570 motherboards or is it specific to your motherboard? Does it also support booting from this adapter?
     
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  13. 386SX

    386SX Master Guru

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    I own some X370 by the way. ;)

    AFAIK it is available for all boards starting with X. X370/470/570.

    See here:
    [​IMG]
    I guess x570 will be the same.

    Please note only Ryzen CPUs without iGPU have enough lanes to do this, as the ones with iGPU have less lanes in total, same as small Athlons.
     
  14. pattakosn

    pattakosn New Member

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    I hadn't come across this, thank you very much! I am going for an x470 or x570 and >= 3600 so I think I will have enough lanes. Now I need to decide on the ssds :)
     
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