I built a new PC with an ASUS ROG Strix B850-I motherboard and a Samsung 9100 Pro NVMe SSD. My benchmarks are topping out around 7000 MB/s, and CrystalDiskInfo reports the drive's current transfer mode as PCIe 5.0 x2 rather than PCIe 5.0 x4. The motherboard specifications indicate that both M.2 slots support PCIe 5.0 x4. I have already updated the BIOS, manually set the M.2 PCIe link speed to Gen 5, and removed and reinstalled the SSD, but the link still runs at x2. Has anyone encountered this with this board or another PCIe 5.0 SSD, and what should I check next?
2 Answers
A damaged or dirty contact could prevent one or two PCIe lanes from connecting correctly. Reseat the SSD carefully, inspect the connector and drive edge for debris or damage, and test both M.2 slots if possible. If the rear slot lacks enough clearance for a heatsink and gets too hot, use the slot with proper cooling for longer testing, then compare the reported link width. If both slots show x2, the SSD itself or the motherboard may need further testing.
Check the motherboard manual for lane-sharing details and confirm that the drive is installed in the intended M.2 slot. Even when both slots are advertised as PCIe 5.0 x4, certain devices or configurations can affect available lanes. It’s also worth testing the SSD in the other slot to determine whether the problem follows the drive or stays with the slot.
I checked the manual and it doesn’t mention either M.2 slot sharing lanes with the graphics card or another device.
I already reseated it, but the rear slot overheats quickly because there isn’t enough room to install a heatsink there.