Daily, Weekly, Monthly. Tape Is the Primary Way . Buy a top quality tape backup unit and set it to backup your entire system every single night. Use at least 5 tapes, if not 10 or more, and cycle through them. Keeping a special monthly set of tapes for a last day of the month backup is also wise.
Tapes wear out too.
They're made of very thin magnetized plastic. Learn what the manufacturer specifies for an expected life cycle and throw them away at that point and replace 'em. Verify Your Backups Regularly. Backup systems that are not working often look like they are. Be sure to use top-quality network backup software specific to the network operating system you are using.