Carbon Copy Cloner (CCC) is the best tool for cloning, synchronizing, and backing up hard disks on Mac OS. You can use it to perform scheduled tasks, incremental backups, full disk clone restoration, and more.
Software is designed to be so smart that people forget it exists. The interface is simple and easy to configure, but the background is so powerful that you can even set the backup to start automatically when you plug in a portable hard drive.