Rsync does not use delta-transfer algorithm?
I am using rsync to back up my home directory to an external USB drive. My home directory contains a VirtualBox disk file which is about 10 GB. It appears that rsync always copied the whole file, which takes disproportionately long compared to the rest of the backup process.
Shouldn't rsync copy only those parts of a file that were changed? I can't imagine that Windows (which resides in that VDI file) always modifies the entire file when it is run, or does it?!
What can I do to make rsync copy this file faster?
Ubuntu 16.04 'Xenial' 64-bit on a Thinkpad T430s (2356AB2) - Intel Core i5 3320M - 16 GB RAM - on-board Intel Ivybridge graphics