Fast, fault-tolerant program/utility for massive file transfer I'm copying 2 TB from one Thunderbolt external hard drive to a USB3 external hard drive. I started the process using command line program rsync with option -avz but this was very slow. I'm wary of the Finder's copy-paste functionality. What's a fast, fault-tolerant program for copying massive amounts of files from one hard drive to another? 

If your answer is a command line program, please give an example analogous to this:

rsync -avz /Volumes/External_1/ /Volumes/External_2
You may start by trying the drop the z from the command. There is no need to compress the files when transferring locally.  Rsync will do a checksum after copying a file, which means it has to read the file back out from disk which will always be slower than a straight up copy.