Why is BSOD: INACCESSIBLE BOOT DEVICE reported if i put the NVME SSD into a USB enclosure as a boot device?

Question

I installed a Windows 11 24H2 in a NVME M2 SSD, then put the SSD into a M2-to-USB enclosure in order to boot Windows from USB 3.0 port.

However, BSOD: INACCESSIBLE BOOT DEVICE was reported when booting from USB3 port.

I have tried to edit registry HKEY_LOCAL_MACHINE\SYSTEM\HardwareConfig{GUID}\BootDriverFlags as 0x14. It has worked, and system booted into Windows successfully.

I realy would like to know why BSOD: INACCESSIBLE BOOT DEVICE was reported in this case.

Answer 1

Hello Paris Zhang (张鹏鹏),

This error typically occurs when Windows cannot locate or access the boot device due to missing or incompatible drivers during the early boot phase. In your case, moving the SSD from an internal NVMe slot to a USB interface changes the storage controller and transport layer, which may not be initialized correctly by default.

By modifying the registry key BootDriverFlags to 0x14, you successfully instructed Windows to load additional boot-critical drivers, including USB and storage class drivers, early in the boot process. This workaround is effective but highlights that the default configuration does not anticipate booting from external USB-based NVMe enclosures.

For future deployments, we recommend preparing the image with USB boot scenarios in mind or using Windows To Go–style provisioning where supported.

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Best regards,

Domic Vo.