rsync(1) --partial
a fast, versatile, remote (and local) file-copying tool
       By  default,  rsync  will delete any partially transferred file if the transfer is interrupted. In
       some circumstances it is more desirable to keep partially transferred files. Using  the  --partial
       option tells rsync to keep the partial file which should make a subsequent transfer of the rest of
       the file much faster.
source manpages: rsync