How to efficiently update a copy of a large binary file

Question

I have a large file (~20 GB, VirtualBox VM of Windows XP) that I would like to clone to a second computer and then keep synchronized, 1-way, from the primary computer.

Is there a generic way of updating only the changed parts of a binary file?

If there is not a generic tool, is there a specific way to do this for VirtualBox?

Answer 1

How about, well, rsync? It uses a block delta transfer algorithm by default.

Answer 2

I just used xdelta

This creates a diff file that others can download from a server to apply locally. More fiddly than rsync, but you can use this method without having to give your box users access to rsync your server.

Simple install on my mint (debian) computer and worked very nicely:

sudo apt-get install xdelta

then to get the details

man xdelta 

To make the diff, very easy:

xdelta delta b4.2.box b5.0.box b4.2.to.5.0.patch

apparently uses the rsync algorithm