Have a look at this:
If you could afford it the belt and braces would be to have two USB HD's the same size as yout internal, then do a series of images (one for each partition) on one, and a clone on the other.(Acronis True Image) I had a problem with an image (I think because I had not validated it) and was glad of the clone - Which, if you wish, automaticaaly copies the partitions of your internal drive. My routine is to run anti virus and SAS and Malawarebytes, then defrag then run the clone and the images. I find that the drive for images needs frequent defragging if you delete , say the image(s) before last.