Yeah I amended my post earlier to recommend logging with a domain specific unmount script, but I don’t know why they want to do this.
They have umpty jillion terabytes of video on a shelf full of external HDD’s and they want to know what files are on which drives. In the old days we had racks full of mag tapes and had the same issue. It’s not something new.
For info about inotify, try web search.
For text search, you start needing real indexing once you’re over maybe a GB of text. Before that, you can live with grep or SQL tables or whatever.