What Apple’s Disk Utility doesn’t tell you.

I’d recently purchased a new hard drive and so fired up “SMART Utility” to have a look at it out of the box. Annoyingly, the external firewire case didn’t support passing the SMART commands through to the drive, but that isn’t unusual. What was interesting was that SMART Utility reported that the internal drive on my MacBook Pro had failed its SMART tests.

Looking at the detailed information it seemed that the drive had a non-zero (1) “Reallocation event count”. A quick check on the Wikipedia’s SMART page indicated that this is a “potential indicator of imminent electromechanical failure”. Some poking around in the Google study “Failure trends in a large disk drive population” indicated that once a drive has attempted a reallocation event it’s 16 times more likely to fail in the next 60 days.

Despite this indicator of impending failure, Apple’s Disk Utility reports that the SMART status of the drive is verified. So I grabbed a copy of the free open source smartmontools

A check with the local AppleCare provider indicated that drives would be replaced if their SMART status indicated they were failing (ie not yet failed). I’m not sure if this applies to all SMART indications, or only to failures reported by Apple’s tools. In that case it would be to Apple’s advantage for Disk Utility to be less conservative in what it reports as failure in order to avoid having to cover warranty claims (although the drive is probably warrantied by the manufacturer, Apple probably still has to cover some of the costs, such as labour).