So, I spent about 12 hours total yesterday on something I could have solved in way less if I'd been a little less tired and observant. I installed MacOS high sierra on an external SSD for the speed since I have a 27in iMac 2017 with an i5, 580 graphics, and a 2tb fusion drive.
However I didn't know that bootcamping with the external drive would be such a nightmare. It only saw the fusion drive and would not partition correctly no matter what I did. I tried boot camp partitioning a couple times. It eventually screwed up the partitions so bad it wouldn't correct back to one volume through bootcamp OR disk utility(even in repair mode) So I had to to CMD-OPT-R to re download the stock macos for the iMac and then while in recovery mode, open up terminal and put in this string of commands to undo all the madness.
Command:
N=Macintosh\ HD; for d in /dev/disk?; do o=`diskutil info $d`; [[ ! "$SSD" ]] && grep -lqw 'APPLE SSD' <<< "$o" && SSD=$d; [[ ! "$HDD" ]] && grep -lqw 'APPLE HDD' <<< "$o" && HDD=$d; [[ "$SSD" && "$HDD" ]] && break; done; diskutil cs create "$N" $SSD $HDD && diskutil cs createLV "$N" jhfs+ "$N" 100%
(the above needs to be put in verbatim)
Site I got this from : https://discussions.apple.com/thread/7453778
OKAY so, fusion drive is back in one piece I boot from the SSD again back into MacOS. I boot into my VM and then I followed the below guide for the rest.
https://9to5mac.com/2017/08/31/how-windows-10-mac-boot-camp-external-drive-video/
However, the windows disk did not show up in the startup disks in my macs settings. BUT it did show up after rebooting and holding OPTION. It shows up as EFI boot under an orange drive icon. Signifying an external drive I think(not sure on that one). All said and done it was 2am and I finally passed out from exhaustion so I'm mostly just posting this to save anyone else the trouble I went through. I'll also have this on my g-drive permanently here.
