You might also want to monitor the console or system log for disk I/O errors like:
Dec 21 15:09:13 halo kernel: disk0s5: I/O error.
That was the start of trouble (happy holidays
) on my iMac G5 internal drive even though SMARTReporter still reported the drive was okay. Apparently that error indicated a bad sector (or sectors) on the drive, and running DiskWarrior actually made the problem worse. I eventually salvaged a satisfying amount of data from the drive, then ran Media Scanner from SpeedTools Utilities on it. That detected and mapped out more bad sectors than I could count before I gave up and called AppleCare to get a replacement drive. I ran Media Scanner on that drive for a day and it was error-free and has been trouble-free.
There was never any indication of a S.M.A.R.T. error on the bad drive (with several utilities) and I'm
much more attentive to disk I/O errors as a symptom of potential drive failure.