If you're not in the habit of regularly backing up your data, do it now. Cloud storage company Backblaze has made it even easier with insanely cheap storage space that you can connect directly to your NAS. Backblaze B2, which has just left beta, offers cloud storage at $US0.005 ($0.01) per gigabyte. The first 10GB even comes free. The service works similar to Amazon Glacier for half the price. B2 is aimed at developers, even including an API that allows you to backup files and folders with the command line. However, you can also use it to connect to your NAS storage (as the video above demonstrates) to keep a secure copy of all your files off-site.
Downloading your data again costs $US0.05 ($0.07) per GB, which means you won't want to use this to replace your Dropbox any time soon. Think of Backblaze B2 more like a digital safe where you can keep your backups long-term without worrying about them. You won't want to get into the safe every day, but you'll be glad it's there if you ever lose your data.