One of my primary external hard drives is starting to fail. It's the drive I use for almost all of my media, including my iTunes library and probably most importantly, my Lightroom photo library. I decided to upgrade my 3TB drive to a MyBook Duo 8TB to get a high-capacity, mirrored-drive setup.
In doing so, I had a small problem: I needed to copy over 2TB of data to this new drive. If I used the Finder, any hiccup along the way would require me to restart the process. For smaller amounts of data, I would just copy individual subfolders, so if one failed there'd be less to copy. That. Is. Tedious.
After some research, I came across this brilliant, safe, and most importantly, fast method: use rsync! When in doubt, turn to the terminal, right?
I ran this command on my top-level folders to copy from the old drive to the new:
sudo rsync -vaE --progress /Volumes/SourceDrive/TopLevelFolder _ /Volumes/DestinationDrive
A few notes to point out, since I made a few mistakes that weren't readily apparent in the StackExchange answer:
I hope this helps you as much as it helps me. Happy copying!