I am finding the information confusing. Deja Dup Backup is running but delivering error messages about not enough storage space. There are only 2.6 Gb of files in Ubuntu One and the limit is 5 Gb. Deja Dup has been an annoying software which turns itself on more often than scheduled and keeps trying unsuccessfully to create a first backup - more error messages. I don't know what is in the Ubuntu One files or how they got there. Can anyone help without using patronising Linux speak please? I understand plain English best.
Just to explain, Ubuntu One is a file storage and music purchasing service. Deja Dup might put files in your Ubuntu One personal storage, or a hard drive, depending on how you set it up. Anyway, if you have more data that Deja Dup wants to back up, than you can fit based on how much room is left in Ubuntu One, it will cough out errors about space.
If your disk crashes, you can log in to Ubuntu One on any computer(that has internet), preferable a Ubuntu machine. You can then download your files from there, and if you have enough space to DejaDup, restores can be done semi-automatically.
Remember that yo can always plug in a hard drive(external) and set up Deja Dup to backup to there, in DejaDup settings. So, you're not paying for storage, but you DO have a backup, just in case.
Just using Ubuntu One for backup without Deja Dup isn't a great solution. You wont have back dated versions of your files. What happens if you screw something up, sync the changes to Ubuntu One and then realise you made a mistake? You have no previous version to restore.
With Deja Dup, you can have multiple (as long as you have storage space) backups, each one dated.
I currently use Deja Dup to backup to external drive, but I'm considering also using it to backup to Ubuntu One. That way having the convenience and reassurance of cloud storage, but with time dated backup versions.