GreenPat said..
It's not much for the cat after the fact, but a take on it I like to live by: Data you don't have at least two copies of is data you're prepared to lose.
Knock on wood, I haven't got two copies of absolutely everything myself right now, I think it's time for a new backup drive...
A colleague was telling me a story just last week of a friend of his who only had one copy of their PhD thesis. After the best part of a year working on it the file was lost and they had to rewrite it all from scratch. Imagine that!
In the day and age of DropBox, Google Drive, iCloud and SkyDrive. Seriously? Doing a PhD you'd expect some basic knowledge of what year it is.
The biggest problem I have is picking which one to use.
At least email yourself a copy once-in-a-while.
As for big data you just can't lose, like all your photographs and home movies, one backup drive and another off-site you back up once or twice a year or something.
And upload the best photos to Flickr or similar where you can't lose them (do you really need 10,000 photos anyway?).
www.dropbox.com/?landing=dbv2www.Flickr.comsupport.apple.com/kb/ht1427