Copy files in Linux, avoid the copy if files do exist in destination

Problem

I need to copy a /home/user folder from one hard disk to another one. It has 100,000 files and around 10G size. I use sometimes I get some errors due to broken links, permissions and so on. So I fix the error, and need to start again the copy. I wonder how could I tell the command "cp", once it tries to copy again, not to copy files again if they exist in the destination folder.