zettabyte would have the same volume as the Great Wall of China.
The NSA is currently finishing construction on its Utah Data Center, a new $1.2 billion storage facility near Salt Lake City. When it's finished, the data center will be able to hold and process five zettabytes of data, according to NPR.
National Geographic:
http://news.nationalgeographic.com/news/2013/06/130612-nsa-utah-data-center-storage-zettabyte-snowden/