I write my ms directly in Google Drive, and transfer the finished chapters to a word document on my harddisk as I go. Which I print out occasionally, just to be sure. And once in a while I will transfer said document to an external harddisk, too.
The reason I write in Google, is that everything is automatically saved every few seconds, and I can go back and look at my 'revision history' and see what the document looked like five days ago, or five months ago, or three years ago for that matter. Nothing is ever lost. Also, I can write everywhere I am, as long as there is a computer with an internet connection available, which suits me fine - I move around a lot, plus have had my laptop crash more than once (or someone else in my household has grabbed it already!).