Photos taking forever to "Prepare Library"

I have had a few issues with Photos crashing for no reason and as I am running the current version of Mojave I thought I should update the firmware on my Drobo 5D external drive - which is where I store my Photos Library. The Harddrive completed its update so I opened Photos only to be faced with a blank screen and spinning disc (not the rainbow wheel). When nothing happened after a while I tried to quit Photos and the message came up "unable to quit while Photos is creating or preparing a library". I have updated firmware in the past with no issues. I have a large Library (approx. 950GB) so understand things take time. It has been 8 hours now and it is hard to tell if anything has happened. Should I just be patient or is there a way to tell if there is actually a library being prepared. Or should I force quit and try a Photo Repair??