Drive partion

I have a WD My Book Essential 3TB drive, Can I partition my drive without formatting it. I already have data on it.

You should be able to as long as you have enough free space. You didn’t mention what OS you have but sometimes a third party tool like EaseUS http://www.partition-tool.com/  the free version works better than Windows. I’d make sure you have a second copy of your data in case of a problem.

Joe