Robocopy is a Windows command line tool that can be used to robustly copy files. It's a bit similar to rsync on UNIX platforms.
robocopy C:\Folder1\ D:\Folder2\ /MIR /XO
Meaning of the options:
/MIR: Mirrors the source to the destination. /XO: Do not recopy older files. If the destination has a file with a date equal or newer to the source, the source file is not copied again.