A zettabyte is a unit of information or computer storage equal to one sextillion bytes.
1,000,000,000,000,000,000,000 bytes = 10007 bytes = 1021 bytes
To illustrate how much data we are talking about, Cisco has made this skyscraper infographic:
Read their blog post @
http://blogs.cisco.com/news/the-dawn-of-the-zettabyte-era-infographic/