Onedrive offline files setting doesn't seem to work

Yesterday I decided to purchase an Office 365 subscription which of course includes 1TB of Onedrive. I'm planning to use this to have an online backup of my 750GB of pictures. The problem is that Onedrive doesn't seem to recognize the "Make all files online only" options in settings. I've done this setting in both the Modern App and in Explorer but it doesn't work.

The problem is that when I try to copy all my pictures to Onedrive (in Explorer) I get an error message stating that I don't have enough space. It appears that the copying attempts to create offline copies of all files in my Onedrive folder which is on a disk that only has 170GB space remaining. And I don't have a drive with 750GB available unfortunately... I could of course buy another disk, but this seems like a bug in Onedrive doesn't it?

I'm running Windows 8.1 Pro btw.

Did you copy them in Windows Explorer? You should upload it in Internet Explorer. Or other browsers.

Are you sure they have uploaded? 750GB is a huge amount to upload and you can't make a file online-only until it is online. Check in the web view of OneDrive through your browser.

If you find one picture that has uploaded then make it online only in File explorer and see if that works. If it does then it is just a matter of waiting. I can upload about 3GB per day per account to OneDrive so it would take me nearly 9 months to upload 750GB. I hope your internet speed is faster.

Once the a file is uploaded it should go online-only making space to copy the next.

Alternatively you can move your onedrive folder location to your external disk - see Move the OneDrive Folder - Microsoft Community and it will upload from there. It will still take time of course but you will not need to copy them in batches to your C: drive.