From http://labs.google.com/papers/disk_failures.pdf http://labs.google.com/papers/disk_failures.pdf "Out of all failed drives, over 56% of them have no count

From http://labs.google.com/papers/disk_failures.pdf http://labs.google.com/papers/disk_failures.pdf "Out of all failed drives, over 56% of them have no count in any of the four strong SMART signals, namely scan errors, reallocation count, offline reallocation, and probational count." Most drives that fail have no SMART errors. In other words they fail spontaneously. BTW, if you have a drive with even a single error, replace it now or at least make sure you have a spare on hand: "After the first scan error, drives are 39 times more likely to fail within 60 days than drives without scan errors." "After their first reallocation, drives are over 14 times more likely to fail within 60 days than drives without reallocation counts, making the critical threshold for this parameter also one."