A few weeks ago I had a severe issue with my laptop, and posted a question here detailing my issue: Prohibition Sign and Can't Reinstall OS X
Today, a friend of mine was having very similar issues which prompted me to run First Aid using Disk Utility. The message I received was "First Aid found corruption that needs to be repaired" with instructions on how to do so. I then restarted my laptop, and lo and behold, it would load up partway and then just shut off. Restarting several times yielded the same results.
Booting into Recovery Mode once again didn't work — no option to re-install & verify/repair disk on there was useless. Used Internet Recovery mode which proved just as useless. Booted into single user mode and ran "fsck -fy" like last time, except this time I kept receiving "The volume Macintosh HD could not be verified completely." along with Disk I/O errors.
Tried running several variations of fsck_hfs -r /dev/diskxsy to no avail — kept getting Disk I/O errors & the messages "corruption was found and needs to be repaired."
By absolute dumb luck, I came across an obscure fix that worked: https://discussions.apple.com/message/23205771#23205771?ac_cid=tw123456%2323205771
I followed the instructions there and it finally worked. I immediately ran First Aid again, and received the exact same original error message. Obviously, I am terrified to restart my computer or try anything, so I'm at a loss at what to do, other than make a backup. My SMART status is Verified. Any help appreciated!
Best Answer
Based on your other question (which you seem to have posted from a different account) and the circumstances surrounding this one, I feel your hard drive is at very high risk of failure.
I would immediately make a full backup of your hard drive.
Once you've made the backup you should satisfy yourself that all of your most important files have been successfully backed up.
Then, as a minimum, I would do a full reformat of your internal hard drive. However, when you do so, don't pick the easy option. Instead click on Security Options and use the slider to choose how many times you want to write over the hard drive. No need to pick anything too high, just enough so it's not formatted in only seconds but instead writes over the entire hard drive.
I suspect that following this process will fail and you won't be able to securely erase the drive. If that's the case, it's time for you to replace the internal hard drive. This is not too difficult (I'd say about medium difficulty) and you can even choose to upgrade to a SSD if you want.
If, on the other hand, you can successfully securely erase the hard drive, then proceed to re-install your system from scratch. Afterwards you can restore your data from the backup you made (however, do not delete your backup).
Let us know how you go.