delete is a file system operation that will delete a file.
Because the unit of persistent on a file system is the file, you can't delete byte.
If you want to delete byte of your files physically with a file system, you need to:
A ledger is a logical layer of your application above a file system that tracks the status of your data block (deleted or not) so that you don't need to recreate a file for each delete.
The procedure is:
Database application implements this kind of logic.