I am trying to backup my mac for the first time using my external hard drive which is a WD 10EADS External Media hard drive. It is a terabite in size or 1 TB. I have a ton of stuff on there that I do not want to lose. However when I go to time machine and select my hard drive as the backup disc it says reformat required (incompatible filesystem) and asks me to delete my whole hard drive. That is not an option because it would take days to move all of that information and I have no where to put it. What should I do? There must be a way to put my backup mac on my hard drive considering it has like 500 GB left of free space. Can anyone lead me in the right direction or is there a step by step process I need to know so I can use the hard drive to not only keep my files I already have on it but add my backup for my mac? Thanks for your help!