http://bugs.winehq.org/show_bug.cgi?id=7873
--- Comment #15 from Vincent Povirk madewokherd@gmail.com 2010-01-03 16:01:15 --- (A new bug would be nice, as I'd rather stop polluting this one.)
It means that, rather than creating a snapshot file that is a copy of whatever is being opened here, the implementation should only keep track of the changes as they are written. That's not implemented, and it could explain why things are slow.