Crosshair VII Hero: can I effectively use 1 M.2 NVMe and 1 M.2 SATA without losing PICE x16 VGA?

Discussion in 'Motherboards' started by Bageland2000, Nov 15, 2018.

  1. Bageland2000

    Bageland2000 Limp Gawd

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    I'm planning to pick up the ASUS Croasshair VII Hero WiFi board with a 2700X

    https://www.newegg.com/Product/Prod...rog_crosshair_vii_hero-_-13-119-097-_-Product

    I was watching Der 8auer's video on it, and it looks like it has a single, M.2 x4 lane directly tied into the CPU which is awesome. The other M.2 slot steals PCIE lanes from the graphics card if you use it.



    I was thinking that I wanted to use M.2_1 with an NVMe drive, and use the other M.2 in SATA mode just for extra storage. However, based on the manual for the board, it looks like the M.2 slot that can be used in SATA mode is the same one that has the dedicated x4 PCIE lanes going to it. So if that's true, there's no way to use two M.2 drives in any configuration, without sacrificing PCIE lanes to the graphics card? Or am I missing something?

    Manual:
    https://dlcdnets.asus.com/pub/ASUS/...HERO/E13835_ROG_CROSSHAIR_VII_HERO_UM_WEB.pdf
     
  2. luke51087

    luke51087 2[H]4U

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    I thought that was just how x370 and x470 was, 4x direct to CPU, 16 to the video card to give the 20 total lanes, and the other was just through the chipset the 8x 2.0. At most when i used my x370 i used one nvme and the bottom one i used a sata drive
     
  3. Bageland2000

    Bageland2000 Limp Gawd

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    Hmm OK.

    I guess what I'm asking is normally, with 1x NVMe (4 lanes) and 1x GPU (16 lanes), you've maxed out your 20 CPU lanes. If I add another drive in the other M.2 slot, but the second drive is a M.2 SATA (not NVMe) is there a way to do that so that the GPU maintains its 16 CPU PCIe lanes without going to only eight lanes?
     
  4. luke51087

    luke51087 2[H]4U

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    basically if you use a sata m.2 it just disables a single sata port on the board. You still have the full 16 to vid and 4 to the nvme
     
  5. Bageland2000

    Bageland2000 Limp Gawd

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    My last question then is can I use either M.2 slot in SATA mode? Because what it looks like is the only M.2 slot capable of SATA mode is the same M.2 slot with the dedicated 4 CPU PCIe lanes.

    In other words, it looks like I can't use one in dedicated x4 mode and use the other slot in SATA mode.
     
  6. kirbyrj

    kirbyrj Why oh why didn't I take the BLUE pill?

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    You have to pull up the manual and read the fine print. It will tell you exactly what gets disabled when you populate the m.2 slots with each kind of drive.

    AMD Ryzen™ 2nd Generation/ Ryzen™ 1st Generation Processors :
    1 x M.2 Socket 3, with M key, type 2242/2260/2280/22110 storage devices support (SATA & PCIE 3.0 x 4 mode)
    1 x M.2 Socket 3, with M key, type 2242/2260/2280 storage devices support (PCIE 3.0 x 4 mode)

    Then you read the footnote:
    The PCIE_x8/x4_2 slot shares bandwidth with the M.2_2 slot

    Which in this case is the lowest x16 slot (which is only an x8 slot electrically anyway I believe). The problem is every board is different so you have to read the fine print on every single one, and look at the diagrams of the board to see how slots are labeled. I already got burned on this as I tried to use NVMe on a board, but it disabled the secondary x16 slot, so I was limited to one graphics card and couldn't use a RAID controller in the other slot (ASRock X370 Pro4).
     
  7. Dan_D

    Dan_D [H]ardOCP Motherboard Editor

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    What you are missing is this: When you use a SATA based M.2 drive, PCIe switches route the lanes through the SATA Express ports on the motherboard. Its still consuming PCIe lanes, but its taking the ones from the SATA ports instead of somewhere else. This is so that the devices can remain bootable, work in RAID arrays etc. The manual should confirm that the SATA ports share bandwidth with one of the M.2 slots if using a SATA device.
     
  8. Ebernanut

    Ebernanut Gawd

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    The comment above about every board using a different setup is correct, every x470 board I looked at used a slightly different config. I also looked at the Taichi, MSI G7, and Aorus 7 and I believe one gave you the option of using SATA for the second slot and the other used PCIe 2.0 lanes from the chipset so it didn't have to steal any lanes from the GPU slot.

    According to the manual the Crosshair VII only supports SATA mode in the first slot that already has dedicated lanes, I have no idea why they did it that way though.
     
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  9. Dan_D

    Dan_D [H]ardOCP Motherboard Editor

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    That's not generally how its done, but then again AMD chipset based boards are a bit strange.
     
  10. Bageland2000

    Bageland2000 Limp Gawd

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    This is exactly what I was confused about and it also makes no sense to me. If I want to use a SATA mode M.2, I want to do it on my non-boot drive. Why would they limit that feature to the primary M.2 slot!?
     
  11. kirbyrj

    kirbyrj Why oh why didn't I take the BLUE pill?

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    I don't know that it really makes a difference though unless you really need to use the bottom x16 slot. You can run PCIe SSD in the lower slot and then SATA in the upper one. Using both slots will drop the second x16 slot from x8 to x4 bandwidth.
     
  12. Dan_D

    Dan_D [H]ardOCP Motherboard Editor

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    PCIe lane switching limitations. It costs more to have switches to allow for increased flexibility.
     
  13. Bageland2000

    Bageland2000 Limp Gawd

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    Der 8auer's video seemed to say otherwise.

    I'm only running a single GPU. Will that run at 16x even if I run both M.2's in NVMe?
     
  14. kirbyrj

    kirbyrj Why oh why didn't I take the BLUE pill?

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    I just looked at the manual here's what it says:
    AMD Ryzen™ 2nd Generation/ Ryzen™ 1st Generation Processors
    2 x PCIe 3.0/2.0 x16 (x16 or dual x8) *2
    AMD X470 chipset
    1 x PCIe 2.0 x16 (max at x4 mode)
    2 x PCIe 2.0 x1

    Then in the footnote:
    The PCIE_x8/x4_2 (the second slot) shares bandwidth with M.2_2 slot. PCIE_x8/x4_2 slot will run in x4 mode if M.2_2 is enabled in PCIe mode.

    The three PCIe x16 (physical size) slots are labeled as follows in the manual:
    Top: PCIE_X16/X8_1
    Middle: PCIE_X8/X4_2
    Bottom: PCIE_X4_3

    Here's a link to the manual:
    https://dlcdnets.asus.com/pub/ASUS/...13834_ROG_CROSSHAIR_VII_HERO_WI-FI_UM_WEB.pdf

    I'm not sure off the top of my head if any use of the second slot bandwidth will drop the top slot to x8 mode or not.
     
  15. Bageland2000

    Bageland2000 Limp Gawd

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    OK Awesome. I read through the manual pretty thoroughly already, but the concise way you put it seems to make it clearer. Namely, I can put a second NVMe drive in and not steal PCIe lanes from the primary PCIe slot.
     
  16. Bageland2000

    Bageland2000 Limp Gawd

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    Nope, nevermind. Look at the graphic at 1:14 in the video. Using the second M.2 slot does take lanes from the primary PCIe slot
     
  17. kirbyrj

    kirbyrj Why oh why didn't I take the BLUE pill?

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    Check my PM. I might have a solution for you.

    I think its a limitation of the X370/X470 chipset. Some boards I've used completely disable the second graphics slot if you use ANY NVMe drive.
     
  18. Bageland2000

    Bageland2000 Limp Gawd

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    Got it. I still don't understand why they would chose M.2_1 as the only SATA-capable M.2 slot, instead of allowing M.2_2 to be configured as SATA...
     
  19. Ebernanut

    Ebernanut Gawd

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    This is correct, section 3.6.5 says this:

    M.2_2 PCIe Bandwidth Configuration

    [Auto]Auto-detects the M.2_2 slot. If an M.2 device is detected,
    PCIEX16_1 and PCIEX8_2 will run at x8/x4 mode, respectively.

    [Disabled(X8 mode)]
    Disable M.2_2 for PCIEX16_1 and PCIEX8_2 running on high
    performance. (x16 or x8/x8)

    [Disabled(X4/X4 mode)]
    Disable M.2_2 with PCIEX8_2 running on x4/x4 for PCIE Raid
    card.

    I agree that logically it would make more sense for the second M2 slot to be able to use SATA so it probably is cheaper to do it the way they do.
     
  20. Dan_D

    Dan_D [H]ardOCP Motherboard Editor

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    Like I said, it has to do with PCIe lane switching. You need extra switches to have that kind of control. Those cost more money.
     
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  21. Ebernanut

    Ebernanut Gawd

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    I was agreeing that it's probably due to cost savings. I'm not sure why it would cost more to offer it on the second slot instead of the first but your comment was admittedly above my pay grade so I'm probably missing something(which is why I didn't address your comment directly :)).
     
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  22. Dan_D

    Dan_D [H]ardOCP Motherboard Editor

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    Got it.

    As for the reason why it was cheaper to do on the primary PCIe slot, its hard to say as many specific details about a motherboard's design aren't provided by the manufacturers. However, I can make an educated guess. Given the M.2 slot's location, I'd say its due to shorter trace layouts and the fact that the primary PCIe slot is already designed to be split in an x8/x8 lane configuration at the CPU. Using PCIe lanes allocated to the PCH or other devices would require additional switching hardware.
     
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  23. Bageland2000

    Bageland2000 Limp Gawd

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    I'm considering adding a second, much smaller NVMe drive for my wife to boot from. Is there any way to add this so that it won't be "used" when booting from the primary drive, and wouldn't steal lanes from the GPU when not in use?