According to the Gartner IT Key Metrics Data 2012 report, the total cost of storing and managing one petabyte of information is nearly US $5 million per year. This means that a large enterprise saddled with 10 petabytes of data is spending about US $50 million per year and could be allocating as much as US $34.5 million of this to data with no business value

You can read more at Information Economics: Making the Case for a Modern Retention Schedule – Journal Author Blog