Reserving space on iOS

I was trying to create a large dummy file on iOS, to reserve some disk space. I created such file using fileHandle.truncate(atOffset: Self.initialSpaceReservation). And it kinda worked - file is created, and FileManager shows it's size as a real deal. But it doesn't take any near it's given disk space on the iOS, when checking Settings. Is this something that system does - compresses empty files? Is there any way to actually reserve disk space like so?