Would that have given any more control than
slippy:~ bruce$ killall -HUP Finder
slippy:~ bruce$ killall Finder && open /System/Library/CoreServices/Finder.app
or various other command lines that purport to be able to restart an atrophied Finder?
I'll jiggle with the disc a bit more once it's finished a lengthy copy operation in progress.
More info: if I mount the massive drive from OSX as a windows share it deals with it all fine. If I try and boot with it plugged in to the Mini, it won't boot (on one out of one occasion -- will try again shortly).
Thanks for your assistance :-)