Booting Issues with Samsung T7

Overview

Recently since updating the BIOS to version: PRIME-X670E-PRO-WIFI-ASUS-3287 there seems to be a timing issue. When the machine is powered on and the BIOS is initialising, then most times it fails to detect the T7 and thus the boot order changes with the only detected drive being the internal NVMe drive which has a EFI partition for Windows only.

This results in the machine failing to show the systemd-boot menu that would allow me to choose between Windows and Arch Linux.

Symptoms

BIOS fails to detect Samsung T7 USB drive during POST approximately 70% of boot attempts
systemd-boot menu does not appear when T7 is not detected
Only Windows EFI partition (on internal NVMe) is accessible
Issue began after BIOS update to version PRIME-X670E-PRO-WIFI-ASUS-3287

Environment

Motherboard: ASUS PRIME X670E-PRO WIFI
BIOS Version: 3287
USB Drive: Samsung T7
Boot Manager: systemd-boot
Operating Systems: Arch Linux (T7), Windows (internal NVMe)

Root Cause Analysis

Hypothesis 1: USB Initialization Timing

The BIOS POST process completes USB enumeration before the T7 is ready to respond.

Evidence:

Issue is intermittent (~70% failure rate)
T7 was consistently detected after Secure Boot key resolution
Fast Boot delay settings have no effect

Tested Solutions:

Increased delay at:
Advanced > Boot > Fast Boot > Fast Boot Delay Time
Result: No improvement
Disabled Fast Boot at:
Advanced > Boot > Fast Boot > Fast Boot
Result: No improvement

Hypothesis 2: BIOS Regression

The 3287 BIOS update introduced a timing regression in USB device enumeration.

Evidence:

Issue began immediately after BIOS update
Previous BIOS version did not exhibit this behavior

Workarounds

Next Steps

Test previous BIOS version to confirm regression
Check for BIOS microcode/AGESA updates
Test alternative USB ports (direct motherboard vs. front panel)
Monitor Samsung T7 firmware version
Contact ASUS support with findings

Secure Boot Configuration — Previously resolved Secure Boot key issue

Timeline

2025-12-17: BIOS updated to 3287
2025-12-19: Secure Boot keys resolved, T7 detection stable
2025-12-20: Intermittent T7 detection failures began

References

Update 2025-12-21

Following a series of other issues derived from the BIOS update, I noticed that the T7 seemed to be stugging on U32G2_20 port, where the disk would show intermittent connectivity issues. I moved the T7 to the U32G2_4 port and since then it has been stable further testing is required though.

The second issue I found was not related to the BIOS. Since Windows 11 and Arch Linux boot from the Linux EFI partition on the T7, I found that Windows updates were modifying the EFI boot entries and thus systemd-boot was being ignored. So when the drive did start to function again, it was masked by Windows automatically loading instead of seeing the systemd-boot menu.