I would expect some discrepancy between "Size" and "Size on disk" in Windows Explorer due to file system allocations etc.
Below is a screenshot of an example file on a Windows 2012 R2 file server that has a 81.4 MB "Size" but for the "Size on disk" it's 0 bytes. What gives?
I have other files doing the same, but yet another set of files and folders behaving as expected showing the size on disk relatively close to the actual file size.
The volume is a basic disk, formatted with NTFS and the default 4K allocation units. No compression is set for any file or folder on the volume. (For those more paranoid, I did a malware scan, and also confirmed there is not ADS streams associated with the file in question).
The user account running Windows Explorer is the domain administrator, and the file owner is also the domain administrator.
Thanks for reading!