thanks for the quick reply i know what i have done wrong . i don't want to back up drive L. that is my problem
You need to answer the original question and explain exactly what you are doing. I know of at least 3 different ways to "backup". What utility are you using, how are you setting it up, etc....?
Before you answer, most backup utlities allow you to select which folders to backup. If your are using Easy Transfer Wizard, go to Custom-Advanced and deselect the External drive.