I have an ASUS ROG Crosshair X870E Glacial motherboard, a Ryzen 9 9950X3D2, and an RTX 5090. I recently bought three 4TB Samsung 9100 Pro M.2 SSDs and would like to install all of them for storage. Can I populate the motherboard's three onboard M.2 slots without reducing the GPU's PCIe bandwidth or causing other performance issues? I'm not interested in using the included DIMM.2 module, but I'm having trouble interpreting the motherboard's lane-sharing information.
3 Answers
You can install drives in all three onboard M.2 slots without taking lanes away from the GPU. However, the second M.2 slot shares PCIe lanes with the USB4 controllers. Depending on how you configure it, that slot may run at PCIe 5.0 x2—roughly equivalent to PCIe 4.0 x4—or the USB4 ports may be disabled. The third onboard slot is limited to PCIe 4.0 x4. So the GPU should be fine, but you may have to choose between full-speed USB4 and maximum bandwidth for the second SSD.
The included ROG DIMM.2 module is probably the better option if you want all three SSDs while preserving the board’s USB4 functionality. Using the appropriate onboard slots together with the DIMM.2 slots avoids the more problematic lane-sharing arrangement. The DIMM.2 sockets themselves have different limits, though, so check the manual before deciding which drive goes where.
The motherboard specifications and lane-sharing diagram are the important parts here. Installing three drives will not automatically slow down the GPU, but one of the onboard sockets can share resources with USB4. In practice, decide whether full USB4 performance or maximum speed on that particular Gen5 M.2 slot matters more to you. The SSD in the third socket will operate at PCIe 4.0 x4 regardless.
The separate Hyper M.2 expansion card is a different matter: using it can reduce the graphics slot to fewer PCIe lanes. The onboard M.2 sockets and the included DIMM.2 module are the safer choices for keeping the RTX 5090 at full bandwidth.