I'm trying to backup my iPhone 7 to my external hard drive, but iTunes says I don't have enough free space. My iPhone has 210 GB. My external drive has 1.03 TB free. What's the problem? Details: iPhone 7 256GB iOS 11.4.1 (15G77) 210 GB used 2015 MBP OS 10.12.6 WD My Passport Ultra external drive 1.03 TB free iTunes 18.104.22.168 I opened iTunes and pressed the option key to choose the iTunes library I have on the WD. I connected the phone, and selected Back Up Now. It worked for a bit, then displayed this message: iTunes could not back up the iPhone "iPhone" because not enough free space is available on this computer. Removing files and emptying the Trash will free up additional space. What's going on? How can I get this to work?