My wife is power of attorney for her aging parents. Over the years, we have em-massed tens of thousands of their documents which have all been scanned to PDFs. We can't afford to lose them. I keep multiple local backups but decided several years ago to add cloud storage as a last resort disaster recovery. I went with SOS Online Backup and feel relatively secure with them.
SOS Online Backup review - http://www.pcmag.com/article2/0,2817,2371307,00.asp