How Do I Backup A Large File To An External HD Periodically?

[Mousebelt]

I am trying to regularly backup my Calibre Library (one file) on hard drive A to hard drive B. The Calibre Library changes regularly, so I'd like to back it up periodically. I don't know how to update the copy of the Calibre Library without simply recopying the entire 800GB archive. I know there must be a simple way to do this, but I've never done it before.

 

[thx1138v2]

Calibre FAQ: How do I backup calibre?