iTunes says I can't back up iPhone because I don't have enough space...but I do I'm trying to move my iphone data from my old iPhone 5 to an iPhone 6s. To start, I'm trying to back up my iPhone 5 to my Windows 7 computer running iTunes. It connects, starts the backup, but about 15 minutes into it I get a message saying there's not enough space on the computer to do the backup.

I have 582GB free on that drive (It's backing up to the C: drive). 

So, needless to say, I'm confused. I've found a few articles that talk about issues with iCloud and wireless backing up, but this is connected direction to my PC so I don't think that's the issue. 

The official Apple documentation says to "free up space" which isn't the issue, or contact support. So, no real help there, either.
So after much swearing and several hours of fiddling, I finally discovered what the issue was.

Windows appears to have a limit on how many files can exist in a directory tree. iOS backups consist of tens of thousands of individual files. And if you have several backups in your backup folder, we're talking a whole lot of files.

The solution ended up being fairly simple:


find your backup folder on your hard drive
move most (or all) of the backups that are in that folder to a separate folder and/or drive.


Then try backing up again. For me, that solved it and I was able to get the backup to run.