[Nottingham] Just how smart is rsync?

[Camilo Mesias]

Alternatively... what about NOT zipping the VM file, and using rsync
-z on the raw uncompressed version. That might give rsync a better
chance to spot the unchanged bits... and rsync would use its own
compression to reduce the data transferred anyway.

It may be worth a try doing this with rsync --progress on two huge
files you know are the same, to see what the performance can be. For
example I just tried it with an 80M file and it used about 350k
bandwidth to decide the file was identical.

-Cam