Ultra on Mac issues - Read only to WD drive

How do I back up to a new Ultra on a Mac?
No matter what I try I get “cannot unmount Disk!”
I have tried the Disk Utility route and there is no Mac backup software on the hard drive.

Hi there,

Try to partition the drive to be compatible with Mac, this seems to be the issue, here is a helpful link:

Try to use time machine to backup your Mac, this is the backup software that come with the Mac. This link Might be of some help:

Thanks. I had tried to partition yesterday and it was failing, but it worked fine today via the same method.