Your hard drive is corrupt
I have a 2011 21" iMac. A few days ago I kept getting an error message saying 'The disk' could not be read and giving me the option to eject or ignore the message. There was no disc in the drive and whenever I clicked eject the message would simply reappear. I used disk utility and it told me that the hard drive was corrupt and needed to be repaired, that I should reboot in recovery mode to use disk utility to repair it. However, the disk was always greyed out and couldn't even be verified in recovery mode, let alone repaired. Apple recommended, as I'd backed up, that I try and erase the disk - which also proved problematic - and do a clean install before importing a back up from Time Machine. I did this. I didn't even use a whole system from Time Machine, merely imported applications and photos and music etc. The machine seemed fine. I even used Disk Utility again to check the state of the hard drive and it said all was fine. Then, without having installed any new software or done anything, the message about the disk not being read with 'Ignore' or 'Eject' reappeared. I verified the hard drive again through Disk Utility and again it said the hard drive was corrupt and needed to be repaired. Again, in recovery mode I cannot repair the Mac HD as it's greyed out.
Is the hard drive simply faulty and needs replacing? If so, why did disk utility at one stage, probably only for a few hours!, give it a clean bill of health?
Comments
It depends. The system that you brought back from time machine had the corruption happening, but it hasn't happened yet on it. Since it says its fine and then it goes to failed, I don't think it is the S.M.A.R.T. status. Try doing a fresh install and using Migration Assistant to restore the users and files on the Mac, be sure to grab a copy of all your applications from the time capsule first though. I have personally never had a HDD failure on a mac, or a 'the disk' error like you, so I can only guess off what I know.
mount -uw /
fsck -fy
reboot