My everyday laptop HDD is now holding 900 GB.  I have  been backing it up by (1) cloning to a duplicate drive &/or (2) creating an image on a 3.5" HDD which is kept elsewhere.
   Either process works well, except for one thing - either process takes over 2 hours.     Simply copying a 900 GB HDD image from one HDD to another is taking over an hour, and this is only at the OS level, not involving the actual cloning/imaging software. 
   I suspect the limitation is the bit transfer rate between the HDD's and not in the cloning or imaging software.   A bulk data transfer seems to be about 50% of the problem.
   I would be willing to invest a bit to buy hardware that can do this job in less than an hour, such as dedicating a motherboard/CPU with at least 2 SATA3 ports linking the HDDs to speed up the transfer (if doing that would help).  I have a couple of old desktops, but they are limited to SATA2 ports.