I would never depend on one backup. I back up my works at least once daily, often twice, to Google Drive, Dropbox, an SD card, a networked computer’s hard-drive (which I back up to an external hard-drive), and then I throw in the occasional email of my WIPs to a secondary and tertiary email account and a DVD backup.
I also copy my main works directory monthly to create a monthly snapshot of it on my main writing computer’s hard-drive.
This all works like a charm and doesn’t take me but seconds to do. I use Spacejock Software’s yCopy2 and saved jobs to make doing these backups simple and quick. It’s as easy as clicking a shortcut link for each backup I want to run.
After every day’s work, I copy my WIP files to a backup directory so that I have a complete daily record of what I’ve written (or deleted). If I work on a WIP for 80 days, then I end up with at least 80 copies in the backup directory. I say “at least” because if I take a break, sometimes I back up then too, and if I know I’m about to do any kind of editing or redrafting, I back up then.
I regularly check that my copies of these files are present where they’re supposed to be and that they open without any problems.
That’s how I back up my writing.
As far as backing up other files: pictures, letters, emails, program settings, even my Calibre library of nearly 800 ebooks? I don’t even bother. It’s kind of funny. I really need to get on that…