Hi 95SLE.
Welcome to the Norton Community Forums. :smileyhappy:
I assume that the only thing you are using the external drive for is the N360 backup. Can you confirm that? If not how much space is being used for other purposes and what in principle are they?
What folders do you find on your external drive? Can you post a screen shot? Tips on how to post screenshots (thanks to Yaso_Kuuhl) can be found here.
When you say " In the N360 back up folder I can only see 30gb of files" how did you get that 30 GB figure? Was it by selecting Preview or Restore, or how?
How long have you been using N360 for backups? How many backup sets do you have and have you used this drive for any previous N360 backups, prior to your current machine?
Sorry about all the questions but hopefully with answers to the above we may be able to move forward. At the moment I would not recommend a re-format but I would suggest that you set your backup "When" to manual until we have sorted this out.
I look forward to hearing back from you.