Hard Drive issues

Ok I seen this asked in the forums somewhere but I can’t find it for some reason, so forgive me for asking agian. I disonnected my hard drive to load more movies and when i connected it to my PC it erased more than half of  my movies, but they are still on the HUB’s drive, so do i have to reconnect the drive to get the movies back? and why were they copied to the HUB I thought they jusy sync through?