Question:

Why is my NVMe drive in M.2 slot 1 only using 2 PCIe lanes instead of 4?

I have a WD SN850X NVMe drive connected to M.2 slot 1 on my Asus 650E-F motherboard, which supports PCIe Gen 5 x4 for that slot. However, when I run CrystalDiskMark, I get half the expected speed for the drive. I checked with WD’s tools and it shows that the drive is only using 2 PCIe lanes. This is not the case for my other identical drive in M.2 slot 2, which uses 4 PCIe lanes and runs at full speed.

According to the motherboard manual, M.2 slot 1 and 2 are both dedicated from the CPU, which is a 7800X3D with 24 PCIe lanes. There is no mention of any lane sharing or switching between the slots or the primary x16 slot. I have updated the firmware of both drives and the BIOS of the motherboard. I have also tried different settings for the M.2 slots in the BIOS, such as auto, gen4, and gen5, but none of them make any difference. I have also removed all other components from the system except for the CPU, memory, and one NVMe drive for troubleshooting purposes.

I don’t know if this is a new problem or if it has always been there. I noticed it after reinstalling Windows 11 on the system. I wonder if there is any way to fix this and make the drive use 4 PCIe lanes in M.2 slot 1. Any suggestions or explanations would be appreciated.

Answer:

This is a puzzling problem that seems to affect some users of the Asus 650E-F motherboard and the WD SN850X NVMe drive. There are several possible causes and solutions for this issue, which we will explore in this article.

Possible Cause 1: BIOS Settings

The first thing to check is the BIOS settings for the M.2 slots. The Asus 650E-F motherboard supports PCIe Gen 5 x4 for M.2 slot 1 and PCIe Gen 4 x4 for M.2 slot 2. However, some users have reported that the BIOS may not detect the correct PCIe generation for the NVMe drive and may default to a lower one, such as Gen 3 or Gen 2. This could result in the drive using only 2 PCIe lanes instead of 4, as each PCIe generation has half the bandwidth of the previous one.

Solution 1: Change the BIOS Settings

To fix this, you need to change the BIOS settings for the M.2 slots to match the PCIe generation of your NVMe drive. In this case, since you have a WD SN850X NVMe drive, which is a PCIe Gen 4 device, you need to set the M.2 slot 1 to PCIe Gen 4 x4 in the BIOS. To do this, follow these steps:

• Restart your computer and enter the BIOS by pressing the Delete key during the boot process.
• Go to the Advanced tab and select the Onboard Devices Configuration option.
• Find the M.2_1 Configuration option and change it from Auto to PCIe Gen 4 x4.
• Save and exit the BIOS by pressing the F10 key and selecting Yes.
• Restart your computer and check if the NVMe drive is using 4 PCIe lanes now.

Possible Cause 2: Windows 11 Settings

The second thing to check is the Windows 11 settings for the NVMe drive. Windows 11 has a new feature called DirectStorage, which is designed to improve the performance of NVMe drives for gaming and other applications. However, some users have reported that DirectStorage may interfere with the PCIe lane allocation for the NVMe drive and may cause it to use only 2 PCIe lanes instead of 4.

Solution 2: Disable DirectStorage

To fix this, you need to disable DirectStorage for the NVMe drive. To do this, follow these steps:

• Open the Settings app by pressing the Windows key and I key together.
• Go to the System section and select the Storage option.
• Find the DirectStorage option and toggle it off.
• Restart your computer and check if the NVMe drive is using 4 PCIe lanes now.

Possible Cause 3: Hardware Defect

The third thing to check is the hardware condition of the NVMe drive and the M.2 slot. It is possible that there is a physical defect or damage in the NVMe drive or the M.2 slot that prevents the full PCIe lane connection. This could be caused by improper installation, overheating, dust, or other factors.

Solution 3: Replace or Repair the Hardware

To fix this, you need to replace or repair the faulty hardware component. To do this, follow these steps:

• Turn off your computer and unplug the power cord.
• Open the case and locate the NVMe drive and the M.2 slot.
• Carefully remove the NVMe drive from the M.2 slot and inspect it for any signs of damage, such as cracks, burns, or bent pins.
• If the NVMe drive looks fine, try inserting it into another M.2 slot on the motherboard or another compatible device and see if it works properly there.
• If the NVMe drive still does not work or shows signs of damage, you may need to replace it with a new one or contact the manufacturer for warranty service.
• If the NVMe drive works fine in another M.2 slot or device, the problem may be with the original M.2 slot on the motherboard.
• Inspect the M.2 slot for any signs of damage, such as cracks, burns, or bent pins.
• If the M.2 slot looks fine, try inserting another NVMe drive or device into it and see if it works properly there.
• If the M.2 slot still does not work or shows signs of damage, you may need to replace or repair the motherboard or contact the manufacturer for warranty service.

We

hope this article has helped you solve the problem of your NVMe drive only using 2 PCIe lanes instead of 4. If you have any questions or feedback, please leave a comment below. Thank you for reading.