iMac Disk Utility First Aid Failed

markbyrn used Ask the Experts™
I have an iMac 27" Retina 5K (Late 2015) El Capitan (10.11.2) and Windows 10 via Bootcamp.   This morning after I had finished some work on the Windows side of the machine, I tried to boot up into El Capitan but it silently failed and the machine turned itself off at about the 2 minute point.  Tried again and same problem.  So I checked if I could get back into Windows and ran Windows 10 with no problem.  Next I booted into the Mac recovery partition to run Disk Utility and it revealed an enormous number of errors on the Macintosh partition such as:

- Previous ID in a hard link chain is incorrect (ID = -1130612101)
(it should be 3164355194 instead of 0)
Many of the above errors appeared with different numbers
- Volume bitmap meds minor repair for orphaned blocks
- Invalid volume free block count
- Volume header needs minor repair
- Missing thread record (id = -1130634630)
Many of the above errors appeared with different numbers

Finally the process 'finished' with "First Aid process has failed.  If possible back up the data on this volume"

Next I booted into a USB installed version of El Capitan and while that was successful, it gave a warning when it mounted the volume that I was having the problem with: "OS X can't repair the disk 'Macintosh HD'" but I was able to copy files from that volume and even run applications that were stored on it.  Tried running Disk Utility and First Aid again but failed as above.

So here are the questions.

1.  Should I assume there's nothing else that can be done other than erasing that partition and reinstalling El Capitan?

2.  Will erasing the partition and reinstalling El Capitan affect my Bootcamp partition or ability to use Win 10?

3.  I have a Time Machine backup; will restoring it re-introduce the same problem?

4.  I've never had such a massive and unrecoverable failure on a Mac drive and I had used it the night before with no problem.  Should I assume the disk itself is faulty and have it replaced?  I ran an Apple Hardware Test and no problems were indicated.
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Since the hardware test didn't show anything, I'd at least suspect that the disk itself is OK, especially since you can run BC. I'd boot into the Recovery partition and wipe the OS X partition - this should leave the BC partition alone, unless you wipe the entire disk. Then I'd reinstall OS X and recover from Time Machine. While it's possible that the corruption is on TM as well, it might not be and if not, you'd get everything back from the last time you did this. I just did this the other day as a part of a troubleshooting step for some issues I was having with my iMac and it worked really well and I got all my stuff back.

Perhaps after you wipe the partition, you could run the Disk check to make sure the underlying disk is OK. If it still comes up as bad, you may need to see help from Apple.
Forgot... I've never seen this kind of massive corruption either, but then it is just a machine and sometimes things happen.
Sorry, also forgot... as long as you don't wipe the entire disk, BC should be OK and bootable.
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The fact that you have so many major errors is certainly suspicious. One thing you can to do check your drive is to check the S.M.A.R.T. status in your system report as described here:

It should show as "verified". If it shows as anything else, you probably have a failing drive.

(I am not sure whether this is still available in El Capitan as it is now no longer part of Disk Utility.)


Thanks for the comments so far and I did verify SMART status and the Apple Hardware Diagnostic showed no problem.   I tried erasing and installing OS X two times but unfortunately, the Mac drive became corrupted both times after running Bootcamp Windows.   That seemingly being the key to the problem, I removed the Windows partition and installed OS X once more.   I have a feeling that the problem might be related to an application I installed that allows one to access the Mac drive from Windows; it's called HFSExplorer.  That would be a wild guess though and I'll wait a day to see if the drive gets corrupted again without the Windows partition.
That's very possible. If you need to have access to the OS X partition while in Windows you might check into MacDrive. I've used that for ages and have never had problem with it.
David AndersTechnician

Disk Utility repairs the directory, it fails on severe problems. Diskwarrior by Alsoft will very often repair such problems.  I have used it three times in last several weeks to repair directory problems, and one of those recover files because the drive was producing errors that DW reported.
If the problem was caused or worsened by HFSexplorer,  removal would be the only solution.

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