I use a Mac air and currently my photos library (about 400 GB so far) is stored on 2 external hard drives (which are duplicates of each other). I want to store one copy of my apple photos library on line as a unit (as my third back up). Does anyone know if I can copy an Apple Photos Library directly into DropBox Back up (I don't want to use it to access my photos - just as a pure 3rd back up). Also what is the largest file size that one can back up to Dropbox back up? Many thanks