10^14 is bits. When you divide 10^14 by 8 you get 12.5 trillion bytes, or 12.5 TB.

If you have 4x 4TB drives in RAID5, and one fails, then in order to rebuild with a replacement drive, you have to read all data from all surviving drives (3 x 4TB = 12TB).

Here is an example from a manufacturer:

http://www.seagate.com/files/www-content/product-content/con...

They call it "Non-recoverable Read Errors per Bits Read" and then list "1 sector per 10^15". So for every 10^15 bits read they expect 1 sector to be unreadable.