THUNDERBOLT3 EXTERNAL SDD WINDOWS10

I can confirm it is possible to install Windows 10 to said external drive. Windows will boot and run from the drive normally after the installation. I also use a G5 and I tried this with that exact drive model (Samsung X5 500GB).

Some more info and an issue I'm having concerning this topic:

I was able to transfer the OEM Windows 10 system which shipped with the laptop to the external drive - I had to make Windows bootable from AHCI first using the Safe Mode method. It boots and runs normally. Even the original SupportAssist OS Recovery function works and will revert to the factory image, although I did have to slipstream an NVMe driver to the factory .swm image first to make it bootable from the X5 - the factory image was installed in RAID mode.

What I did not manage to do yet is to successfully transfer a clean installation of Windows 10 on the internal NMVe drive to the external NVMe drive. I had installed Windows 10 in RAID mode, so I made it AHCI bootable in Safe Mode as with the OEM OS and figured that should be enough to make it bootable from the external drive, but I was obviously mistaken: Once transferred to the X5, Windows will boot straight into "Preparing Automatic Repair" mode and fail to repair anything. I've tried to solve the issue for a couple of days now but have not been successful. I'm out of ideas at this point, so if anyone has any info on how to do this I would very much appreciate it. Cheers.

Ok, after closer examination it seems the imaging software I'm using, which is somewhat dated, is unable to cope with the 4K sectors of the X5: Partitions are aligned since the software uses the LBAs of the X5, but the file systems it creates obviously don't. I've tried several other up-to-date disk imaging/cloning programs without success. For whatever reason, cloning the OEM system works, but not a clean installation of Windows 10.

I should note that everything works normally when cloning the OEM disk to the X5 except for the Device Encryption feature - this becomes broken on the external drive.

The performance of the X5 is actually higher than the factory original internal NVMe drive (an SK hynix BC501 in my case) - it's quite impressive, actually.

As I suspected, it's the file systems the imaging software produces which was the problem: Not to get too technical, but the software reproduces the original MFT zone start and end values of the file systems it copies, which are incompatible with the X5. These numbers happen to line up for the OEM image. Also, the original EFI system partition (99MB), which the imaging software also reproduces, is too small to fit a FAT32 volume on a disk with 4K sectors, resulting in a corrupt volume. I was able to circumvent the problem by using the partition structure created by the Windows installer on the X5, formatting each partition using the OS formatting utility and copying the contents of the original partitions to the new ones. It's a somewhat cumbersome and time consuming procedure, but less so than having to reinstall Windows from scratch, along with the slew of software and settings I had already installed on the internal drive.

Don't know if Dell's engineers purposefully installed the OEM system with MFTs that are compatible with both legacy and 4K disks, but kudos to them if they did

BTW, in answer to the query about why you would want to use an external boot drive rather than the internal one, here are a couple of reasons:

1. It's easy to switch external drives to run different OSs and configurations.

2 It's easier to replace the external drive when it goes kaputt.

3. It's simply cool

You can add less thermal build-up inside the machine and data safety to the list - It's easy to store an external system drive separately from the laptop, in case the latter gets stolen.