External Hard Drive making my mac slow

I am looking at my imac’s activity monitor and it says the WDSmartware is running 200% of CPU when plugged in and about 99% when not. When plugged in my computer is all but useless. What should I do. I need to edit my photos, but theres nothing I can do. Is there a way to restart this thing? Thanks in advance.

You can uninstall smartware if you are not using it. 

http://wdc.custhelp.com/app/answers/detail/a_id/5373