A little over a year ago, Ancestry.com was managing about 4 petabytes of data, including more than 40,000 record collections with birth, census, death, immigration, and military documents, as well as photos, DNA test results, and other info. Today the collection has quintupled to more than 200,000 record collections, and Ancestry's data stockpile has soared from 4 petabytes to 10 petabytes.
NOTE: A petabyte is equivalent to 1,000,000,000,000,000 bytes or 1,000,000,000 megabytes or 1,000,000 gigabytes or 1,000 terabytes. However you measure it, a petabyte is a lot of data!
Jeff Bertolucci's article may be found at http://goo.gl/sHzU1a.