New
#11
To avoid confusion:
C and D are internal?
How large is the external and what is its purpose?
Generally, until I see more details, I'd think in these terms:
Make an image of C. That will contain your OS and ALL of your data. Store the image on D and possibly also on your external.
There is no reason to image D.
Backup the data portions of C to D and/or to your external by normal means, NOT using an image.
Do not rely on an image for data backup. Images are known to be flaky at the worst possible moment.