Bootcamp tends to install onto the slowest portions of a fusion drive-- and under certain conditions-- it can be slow as molasses. So, I installed my copy of windows onto a external SSD. A USB3 drive, in fact/ (Which required me to manually construct the partition map, and do ...other things, since windows doesn't like to be installed to a USB3 drive) When I want to use my specialized CAD program, I hold down down the option key and select the EFI partition. The problem occurs when I update windows. Somehow, whenever I reboot after an update, the list of available bootable drives is truncated. My external drives, including the all important EFI drive do not show up. And so, when boot into OSX-- and reboot into windows, windows update "knows" that the process has been interrupted, and marks the update process as failed. Does anybody know what's happening? I have a 2014 imac 5k, with Windows 10 Home, and the usual High Sierra.