I was wondering if Dropbox works like git/rsync in that it deltas the files against the local repository in order to only send the changes to the files across the link.For instance, if I put a 1GB file in the Dropbox folder and sync it with Dropbox, then make a change to it and now its 1.2GB. When syncing, will Dropbox send the whole 1.2GB across or just the .2GB?
When does Dropbox delta?
dropbox
Answer by Moo at Serverfault:Dropbox uses a binary diff algorythm to break down all files into  blocks, and only upload blocks that it doesn't already have in the  cloud. All of this is done locally on your computer.Dropbox doesn't just use your files that you have already uploaded, it  aggregates everyones files into one database of blocks, and checks  each local block hash against that database.This means that if someone else has uploaded the same file as yourself  (say for example, the latest Ubuntu iso), then the upload will seem  instant as there is nothing to upload, but if you are updating a file  that changes regularly, like your backup file, then only the changes  are uploaded. If you upload a totally unique file, then you have to  wait for it all to upload.