It's about half as much as Mozy.
In other words, the amount of Mozy is 2 times 21 petabytes.(2009 figures) (total file storage)
Mozy, the online data backup service, stores about 50 petabytes of data backed up its users. Founded in 2005, Mozy's customer base has grown to 1 million personal and 60,000 business subscribers in just 5 years.
It's about three-tenths as much as The Books in the Library of Congress.
In other words, the amount of The Books in the Library of Congress is 3 times 21 petabytes.(2009 figures) (digitized entire collection)
The total collection of books, photographs, and other media housed by the United States Library of Congress would occupy about 70 petabytes if fully digitized. The collection contains a total of 142,544,498 items as of 2009.
It's about five times as much as The Letters Delivered by the Postal Service in 2010.
In other words, the amount of The Letters Delivered by the Postal Service in 2010 is 0.20 times 21 petabytes.(2010 figures)
All letters delivered by the United States Postal Service in 2010 will equate to 5 petabytes (pB) of data if stored digitally. In delivering the mail, the Postal Service fleet travels a total of 1.25 billion miles annually.
It's about six-and-a-half times as much as Netflix's Watch Instantly catalog.
In other words, 21 petabytes is 6.690 times the amount of Netflix's Watch Instantly catalog, and the amount of Netflix's Watch Instantly catalog is 0.1490 times that amount.(May, 2013 figures)
The uncompressed source copies of all the movies available for instant viewing on Netflix total 3.14 petabytes. According to estimates, videos streamed from Netflix account for about 29% of all Internet traffic
It's about eight-and-a-half times as much as a Human Brain.
In other words, the amount of a Human Brain is 0.120 times 21 petabytes.According to Northwestern University psychology professor Paul Reber, the capacity of the human brain is a theoretical 2.5 petabytes. Each lobe of the brain consists of folded neural tissue with a total area, if unfolded, of about 0.24 sq. m.
It's about eight-and-a-half times as much as The US Census Bureau.
In other words, the amount of The US Census Bureau is 0.120 times 21 petabytes.(a.k.a. United States Census Bureau, a.k.a. Bureau of the Census) (2010 figures) (total active data)
The United States Census Bureau administers 2.5 petabytes (pB) of demographic and population data gathered through the decennial census and other surveys. The Census Bureau makes the results of each census public 72 years after they are gathered.
It's about ten times as much as an Imgur's Monthly Bandwidth.
In other words, 21 petabytes is 9.980 times the amount of an Imgur's Monthly Bandwidth, and the amount of an Imgur's Monthly Bandwidth is 0.10 times that amount.(Jan-Feb, 2012 figures)
Imgur, the free online image hosting service, used a total of 2.11 petabytes in bandwidth between January and February, 2012. The site has served up over 15 billion images in that time.