Duplicate External Hard Drive With Multiple Partitions

I've been searching over a few days and can't seem to find a definitive answer. What I'm trying to do is duplicate an external HDD that contains multiple partitions. I have two identical 3TB HDDs. One (HDD A) is partitioned in this way: |Parition|Size| |:-:|:-:| |1|2TB| |2|500GB| |3|500GB| The other (HDD B) is blank and I'd make an exact copy of HDD A to HDD B. However, I can't seem to figure out how to do this. I've tired Disk Utility and CCC, but neither seems to be able to do this. Suggestions? If it matters, the reason I'd like to make the copy is for an offsite backup of HDD A.