Purchased Winclone 9 to transfer from internal installation to external SSD.
System stats:
iMac 2020 27", Big Sur installed
External drive - 2TB PNY CS3030 NVME installed in TB3 enclosure (JHL6340 controller)
Partitioned 500GB for boot camp
Tried all of the advice on this forum with no luck.
Getting the same error message with BSOD: INACCESSIBLE_BOOT_DEVICE
Please advise what to try next.
Exactly what I want to do (although I may use a regular hard drive for Windows). I have posted a question on this, which as not been answered. as yet. Your experience does not fill me with optimism, sadly.
I have seen the “inaccessible” message before in virtual set-ups, using the Boot Camp partition, and I had tried every trick in the book, eventually only coming right through a Parallels upgrade. Quite what was going on, I never established. A while back, I had exactly the same problem with VMWare Fusion, and that’s when I switched to Parallels. The Boot Camp partition always booted properly on its own. So, although we are looking at a different problem, this message is pointing to a similar glitch, I would expect.
The issue is most likely drivers since Windows needs the correct driver during boot up for the TB3 enclosure. Since apple doesn’t provide it, it would fall on the vendor to provide it, so it might be worthwhile to check their website. I wouldn’t be surprised if it didn’t exist since there probably isn’t a lot of folks external booting Windows with it. I could be wrong though 
tim
The drive shows up when I load windows thru the internal boot camp installation.
Also, the drive controller is common (Intel’s JHL6340).
I think there’s something else that is causing this… such as TB3 drive mount timing with the boot load sequencing.
I think someone mentioned that it works if the drive is disconnected and reconnected right after the windows boot sequence?
Does this qualify for a refund since I cannot get it to work on my external drive?
Yes. Please request one here:
tim
I have a similar issue except it does the same thing on the internal partitioned drive as it does on the external drive. I get BSOD boot drive inaccessible
Microsoft released an update KB4586853 addressing this error with TB3 NVMe drives. If you still have the external I would install all available Windows updates then try again.
Edit: Hmmm, maybe this is a fix for a different error “ DRIVER_VERIFIER_DMA_VIOLATION”
I got all of the drivers working except my external thunderbolt 3 devices, so this is the issue. The only item in device manager with an issue is “unknown device”. I have tried removing bootcamp drivers and reinstalling and tried Sysprep
I have successfully booted the 2011 iMac (running High Sierra and Windows 10) off the new OWC Thunderbolt 3 Envoy Express with an OWC Aura P12 SSD inside.
2011 iMac -> Apple TB(1/2) cable -> Apple TB2 to TB3 adapter -> OWC Thunderbolt 3 14-port dock -> OWC TB3 Envoy Express NVMe SSD.
Getting faster speeds than with an internal SATA III SSD in the iMac.
Installed UEFI Windows on the internal hdd and used sysprep. Used a DSDT patch with test signing mode to get the audio working.
The mini DisplayPort on the dock isn’t working in Windows but other than that it’s running great.