Most efficient way to back up, then sync, one 2TB drive to another 2TB drive (ubuntu)
 

Hi.
Running ubuntu-mate.
Can any backup experts suggest the best way to back-up, and then perform regular syncs from one 2 TB external drive to another of same size?

rsync is pretty much the standard for syncing one drive/directory to another.

Basic usage would look something like:
You can refer to the man page for the definition of those flags and the others available in rsync. The first time you run it, it will copy everything. From then on it will compare sizes and timestamps to determine if any of the source files have changed, and if so it will update them on the destination.

The first rsync is usually a good time to "go make a pizza or something."
From now on. Forever, until death-do-us-rsync

Consider the above choices but you also have some distro maintained backup programs that may be worth looking at too.