A. A S.M.A.R.T. error is a predictive failure notice. The drive will fail in the near future and should be replaced at the next earliest time possible

B. A S.M.A.R.T. error is a write operation error. It has detected that the write sent to the drive was incorrectly formatted and has requested a retransmission of the write from the controller

C. A S.M.A.R.T. error is simply a bad sector. The drive has marked the sector as bad and will continue to function properly

D. A S.M.A.R.T. error is an ECC error. Due to error checking and correcting, the drive has corrected the missing bit and completed the write operation correctly.