You may find that your system reports that a S.M.A.R.T. error has occurred on the mac hard drive. S.M.A.R.T. errors are a near-term prediction of drive failure. It is important to realize that the drive may appear to be functioning normally. Even some diagnostic tests could still have a PASS status. A S.M.A.R.T. error on the mac is a prediction that the diagnostic test will soon fail.