Solution 1:

I think I found the answer on Process Hacker forum:

They're different concepts. If a process writes to a named pipe, that's I/O, but it has nothing to do with the disk(s) on your computer. Similarly if a process does I/O on a file, the contents don't have to be written out to disk immediately.

So I/O includes every data transfer, while disk read/write can be inacurate.