I have a 1000 gig Windows SATA HD.
I don't want to delete the Windows installation for case I will sell this hard drive with the PC it came with.
Using Gparted, on by Ubuntu 17.10 PC running from a SSD drive, I shrinked the 1000 SATA hard drive so the Windows in left untouched,
Created a 400 Gig partion EXT4
And I can't create Folder within this partition but can see it from the FileManager.
As I can understand, your mount point is named
BackUP
.So you should take ownership of the filesystem with: