Question M.2 SSD not viewable in BIOS when in the M.2 Socket. Can be viewed ( but slow) when in a PCIe adapter in X16_2, not viewable in X16_3 or X16_4.

[Didymus21]

Title pretty much says it all. I have a WD_Black SN 850X that I'm trying to use with my ASUS X-99A. I realize I cannot exceed Gen3 speeds, even though this is a Gen4 SSD. Here's the thing, though...it is not visible when in the M.2 Socket. No option to enable this in the BIOS. If I put it in X16_2, the BIOS does see it and I can manually change the speed to Gen 2. However, if I move my GPU down to X16_3 and put the M.2 SSD with adapter into PCIeX16_1 then I can run it there and manually change it to Gen 3. The GPU performs the same whether in slot 1 or 3. Does this make sense to anyone? I have to move all sorts of things around to get my GPU into the X16_3 slot, so not ideal by any means. Why on earth can't I keep the GPU in X16_1 and put the SSD in X16_3 and still get Gen3 speeds? With this configuration, when I put the SSD in X16_3 the BIOS does not recognize it at all.

Any advice would be greatly appreciated. Whether that be making it work in the dedicated M.2 socket, or figuring out how to make it viewable when in the X16_3 slot. Thanks!

 

[CountMike]

Title pretty much says it all. I have a WD_Black SN 850X that I'm trying to use with my ASUS X-99A. I realize I cannot exceed Gen3 speeds, even though this is a Gen4 SSD. Here's the thing, though...it is not visible when in the M.2 Socket. No option to enable this in the BIOS. If I put it in X16_2, the BIOS does see it and I can manually change the speed to Gen 2. However, if I move my GPU down to X16_3 and put the M.2 SSD with adapter into PCIeX16_1 then I can run it there and manually change it to Gen 3. The GPU performs the same whether in slot 1 or 3. Does this make sense to anyone? I have to move all sorts of things around to get my GPU into the X16_3 slot, so not ideal by any means. Why on earth can't I keep the GPU in X16_1 and put the SSD in X16_3 and still get Gen3 speeds? With this configuration, when I put the SSD in X16_3 the BIOS does not recognize it at all.

Any advice would be greatly appreciated. Whether that be making it work in the dedicated M.2 socket, or figuring out how to make it viewable when in the X16_3 slot. Thanks!

You may be running into a problem or lack of limited number PCIe lanes,
Top PCIe X16 is usually supplied with PCIe lanes from CPU and may also be shared with second OCIe x16 slot. To mix them PCIe has to support bifurcation. Other PCIe slots are getting lanes from chipset but are also limited with number of lanes it can supply also subject to bifurcation if shared.
That also includes eventual M.2 NVMe slots. and anything (like IGPU) that uses PCIe lanes. IGPU usually uses up to 4lanes and those are not available to anything else even when IGPU is not active.
In addition,PCIe supplied by chipset may be one generation earlier than CPU ones which of course affects it's speed.
SSDs even NVME are downward compatible with earlier PCIe and SATA generations