Hi John.
The backup programme I use is called Synkron for all my backup needs to a separate PC setup for the purpose, though the software will also work to a USB drive as required.
The software is totally free for life, works across different platforms and, best of all, is ad-ware, pop-up and virus free.
When run (As Administrator if using Win7) the software looks at previous backups and only backs up files that have changed or are new since the last backup was taken. The only user input required is to tell it which drive to back up and to where, and then only at initial setup, then you simply click "Sync" and the package does the rest.
It's perhaps worth bearing in mind that the initial backup will take some time, depending on how much data you need to backup. Subsequent backups are much quicker as it only backs up changes to the drive and not the entire contents again.
The software can also be set to backup your files according to a schedule set by the user
I have been using Synkron for years and it has never once failed me.
Give it a try, you might like it.
Link: **LINK**