The files are 500Mb and 115Mb and they are open, on and off, throughout the day but probably only for about 30% of the time. What mystifies me is the fact that they are not being backed up and yet the Backup tab in WD Smartware shows a blue tick suggesting that everything is up to date. I would not expect to see this is if, “operations”, to use your term, are still in progress - particularly when it comes to initial switch on at the start of the day.