Want a backup that is reliable?
xcopy c:\documents\*.* d:\ /S /D /Y
This will compare and copy files that have changed and any new copies.
You can also copy this to notepad and make a batch file.
Type the following:
xcopy P:\*.* g:\ /D /s /Y
Substitute the P: and G: with your drive letters and put the folder you wish to copy (this will also copy any subfolders)
Click on File and Save As
Change file type to all and name the file whatever.bat
You can now add this to your scheduled tasks if you want.