Answer by kalikid021 for Bash: mv directory one at a time

Just for reference, I believe the mv command doesn't do a copy then delete operation, ie having

mv /home/foo /home/bar

exist simultaneously for a short period. It operates more like renaming. Essential changing the filesystem accounting so that what pointed at /home/foo now points to /home/bar without actually physically moving the data on disk from one place to another, or copying then deleteing from the previous location.