TL/DR: Proceed with extreme caution.
Heads up for anyone wanting to do a macOS High Sierra clean install plus migration. I’ve been unable to successfully use Migration Assistant to restore my Apps/HomeDir/Settings due to it’s ultra slow speeds.
I tried migration using:
- A HDD backup over USB (created with SuperDuper); and
- Airport Time Capsule TM backup over Ethernet; and
- Airport Time Capsule TM backup over Wifi.
With USB I tried different cables, different USB-C ports, different USB to USB-C adapters, but seeing it also happened over Wifi, I assume it’s a High Sierra bug.
Rolling back to Sierra
Not wanting to do a fresh install plus a piece-meal hand install of all my apps & settings (at this point in time at least), I decided to roll back to Sierra from my USB HDD, but no, that brought about a new set of problems.
Because High Sierra wipes the Sierra Recovery partition, FileVault wont activate. The Recovery Partition is normally created by the Installer, so without going back that five hour step, I ended up using https://davidjb.com/blog/2016/12/creating-a-macos-recovery-partition-without-reinstalling-osx-or-re-running-your-installer/ to successfully rebuild the recovery partition.
And finally, to rebuild the recovery partition, you need the Sierra installer, which Apple in their infinite wisdom have removed from the App Store under Purchased items. Luckily after tearing the house apart, I found a copy on a rogue USB stick.