the –partial option is the one that does the file resume trick, -a option stands for –archive and turns on the archive mode; equals -rlptgoD (no -H,-A,-X) arguments and -v option shows a file transfer percantage status line and an avarage estimated time for transfer to complete, an easier to remember rsync resume is like so:
I can answer only the part about the difference between terminal an nautilus. I have checked several times this. It appears copying from terminal is faster than any graphical way like nautilus. At least in my case, when i copy about 32GB of info, it takes about 3 to 5 minutes less from terminal than nautilus from a 25 minute copy. that is about 10%-20% of the time. About a way to resume a copy to your external unit i think curl or rsync would resume a failed copy. At least with cp command. I have not tried this myself (I wil try tomorrow) but this two might work.
Rsync Resume | | The world of Proposals
Of course for the rsync resume to work remote Linux system had installed rsync (package), if rsync was not available on remote system this would have not work, so before using this method make sure remote Linux / Windows server has rsync installed. There is an rsync port also for Windows so to resume large Giga or Terabyte file archive downloads easily between two Windows hosts use .