External Hard Drive Duplicate

I store my iMovie library on a 1TB external hard drive. Presently, the file is about 550 gb. I would like to regularly back it up with another external hard drive, also 1TB in capacity.
What is the best option for regularly "cloning" or "copying" one external hard drive to another? I know I can delete my backup HD, then copy & paste the file, but it makes me nervous to delete the backup. The backup HD is not large enough for me to leave the older backup on it AND put a newer one on as well.

Carbon Copy Cloner. Download and buy from here. You install it on your Mac and then make a clone of the first external hard drive. Restore the clone to the other hard drive.

So as not to be confusing, what chscag means is to clone FROM the source drive TO the second drive. If you lose one, you can restore from whichever you have to wherever you want. I read his last sentence to say that you clone it, then restore it, but that isn't how CCC works. You just clone FROM and TO.

Yea, thanks for the clarification.