Update September 2018
I read about the most convoluted ways to back up SBC systems…. some back up only data, some use arcane commands to do the job – few if any are a single click job for a complete backup that can even handle larger or smaller SDs. That is except for RPI-Clone.
Below “Original article” was written back in 2016 – things have changed a little since then. Bill Wilson has revamped his rpi-clone project and the current version of this superb command-line tool for the Raspberry Pi is here.. https://github.com/billw2/rpi-clone