Science & Tech · Gadgets & EVs · 2 hrs ago
A BIOS setting limited a USB4 drive to USB 3 speeds
A desktop user found that a USB4 SSD enclosure was transferring files at about 1,000 megabytes per second, similar to a 10-gigabit USB 3.2 connection.
The setup used an ASUS TUF Gaming X870-Plus WiFi motherboard and a Satechi enclosure holding a WD Black SN850X SSD.
Changing cables and USB4 ports did not improve the speed.
The cause was a BIOS setting that had disabled PCIe tunneling, which lets USB4 carry an SSD’s PCIe connection through the cable.
With tunneling off, the enclosure fell back to USB 3.2 mode, and Windows did not warn the user.
Enabling PCIe tunneling in the BIOS restored the USB4 connection, according to the user’s account.
A disabled PCIe tunneling setting in an ASUS motherboard’s BIOS limited a USB4 SSD enclosure to USB 3.2 speeds.
The drive recorded sequential read speeds of 1,013 MB/s and write speeds of 978 MB/s.
The author found the clue in Windows Device Manager, where the SSD appeared as a SCSI disk behind a USB Attached SCSI controller.
Enabling PCIe Tunneling in the BIOS restored the setting needed for USB4 PCIe tunneling.
- Who
- XDA author Shivansh, using a Satechi USB4 NVMe SSD Pro enclosure.
- What
- A BIOS setting disabled PCIe tunneling, leaving the USB4 enclosure running at USB 3.2 speeds.
- When
- The issue was discovered after a BIOS update had fixed warnings that appeared in June. The article was published on October 12, 2026.
- Where
- On a desktop with an ASUS TUF Gaming X870-Plus WiFi motherboard.
- Why
- PCIe Tunneling had been turned off and was not enabled again after a BIOS update fixed Device Manager warnings.
This story does not have two clearly opposing sides.
The real culprit was a BIOS setting I'd switched off months earlier.
With tunneling off, the enclosure falls back to USB 3.2 mode at 10Gbps, and you get exactly the speeds I was seeing.
Plot twist: the bug was me.
Warning icons appeared next to PCI Express Downstream Switch Port in Device Manager.
A BIOS update fixed the warnings, but the author did not re-enable PCIe tunneling.
The author found the drive running at USB 3.2 speeds and identified the disabled BIOS setting.
The author enabled PCIe Tunneling in the BIOS.
- Motherboard
- ASUS TUF Gaming X870-Plus WiFi
- Enclosure
- Satechi USB4 NVMe SSD Pro
- SSD
- 2TB WD Black SN850X
- Read speed before fix
- 1,013 MB/s
- Write speed before fix
- 978 MB/s
- USB link mode with tunneling off
- USB 3.2 mode at 10Gbps
Sources
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