On my NAS I have a file which is 2,14 TB in size. When I connect via FTP, the file is reported as 219 GB or 230.319.792 KB. When I connect via SMB share in DO, the correct size of 2,14 TB is shown. Connecting via Windows Explorer, the file size is shown as 2.303.197.912 KB.
The first 10 digits of the KB size are identical. Some kind of rounding/variable size problem?
I found the source of this behaviour. On the tab "Misc" of the FTP settings I disabled "Use FEAT" and "Use MLST" for a reason I don´t remember. When I switch back to "Use defaults", the file size is shown correctly.