Drive failure rates

http://blog.backblaze.com/2013/11/12/how-long-do-disk-drives-last/
http://static.googleusercontent.com/external_content/untrusted_dlcp/research.google.com/en//archive/disk_failures.pdf

From Backblaze study:

• The company is storing 75 petabytes of customer data on more than 25,000 consumer-grade hard drives.
• It has been in business for 5 years and 74 percent of the hard drives it has ever deployed are still running.
• Annual failure rate for drives is 5.1 percent for the first 18 months, 1.4 percent for the next 18 months, and 11.8 percent during years three and four.

Google study: