How does Dropbox deal with backing up Parallels Desktop images (or vice versa)?

[jim_in_public]

I use Parallels Desktop to run Windows 10 on my MacBook Pro.  The .pvm files that Parallels creates for these disk images can be quite large -- 30 to 60 GB -- so I'm wondering what happens when Dropbox is used to backup the Documents folder containing these files.  I like the idea of having them backed up, of course, but I don't want to kick off a 60 GB transfer every time I do something in my Windows image.  I've done a few tests that suggest this doesn't really happen (files show up as "edited now", which implies a simpler and lower-bandwidth action?  updating individual files down inside the Mac package instead of the whole thing?), but I can't tell for sure.  Does anybody have an experience with this, or have real information about what goes on?  Thanks!

[Mark]

Hi @jim_in_public 

Dropbox will only upload the 4mb blocks which have been changed so it will upload less - obviously the more use that you have within Windows the more files will change and so more upload. The same happens on download side as well. 

BUT! From a safety point of view personally I exclude Parallels from my Dropbox because I dont want it syncing while its open and worry it may not fully upload before downloading to another device and corrupt things.

[jim_in_public]

Thanks much!, and a good point about the syncing issues.  If I do the semi-obvious thing -- right-click on the Finder's view of the .pvm file and pick "Don't sync with dropbox.com" -- what becomes the status of (a) the local copy and (b) the remote, dropbox.com copy?  Does the remote copy stay around for possible re-syncing later?