For iMac 5K or For 2013 Mac Pro
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How to detect a failing hard drive (SMART status)
Checking on drive status
To check on SMART status in Mac OS X, open Disk Utility (/Applications/Utilities) and take a quick glance at your drive(s).
Pending failures will be obvious: the Failing. If a drive has completely failed, it won’t even show up.will read
Unfortunately, the SMART status of drives used in certain external enclosures is not visible to your Mac. An external enclosure and/or eSATA card must have SMART support.
What to do for a failing drive
Take immediate action:
Replace the drive as soon as possible: use overnight delivery for a replacement. Do not delay, it could fail in 2 months or in 2 minutes.