The standard, non-beta El Capitan installer corrupts the HFS+ superblock, and states that it cannot fix the hard drive and cannot continue with installation. (The repair tools won't fix the hard drive even in single user mode.)

What is confusing me is that the backup of the superblock remains valid, and upon writing the backup over the corrupted current superblock the drive appears on the boot options screen again. And I can boot into Yosemite with none of my apps/data are affected.

That said, if I run the installer again it munges the current superblock and leaves the backup still valid. So I can repair the drive again and boot normally. (And continue this process ad-nauseam)

A: Why doesn't disk utility check for the fact that the current and backup superblocks are different. And attempts to test with the backup if it can't otherwise repair the drive. (Even in single user mode)

B: Why does the OSX installer consistently corrupt only the superblock, leaving nothing in the rest of the drive broken. I have done this, including re-downloading the installer, five times at this point. Mostly out of morbid fascination now.

I am testing from

  • Yosemite.
  • 13 inch Mid 2013 Air.
  • Drive un-encrypted.
  • 22GB of HD free.

SSD drive health is reported as excellent.

Any ideas on how I can get out of this cycle? Thanks for any feedback.

PS Tempted to just try the Sierra beta and see if whatever this problem is is patched in the next installer.

Edit: I ended up trying the current Sierra beta, with the exact same results.

  • star & upvote just because I have no clue what you're talking about... but it sounds interesting <g> It's also something that, were it other than a very specific-case repro, would be bound to be common knowledge by now - so i think the underlying issue isn't the OS installer but something to do with the drive itself. I'd be interested to see what something like DiskWarrior thinks of it.
    – Tetsujin
    Commented Jul 16, 2016 at 18:40
  • Thanks. Alas I can't afford DiskWarrior. (Financially or emotionally)
    – BorisKourt
    Commented Jul 16, 2016 at 18:42
  • Emotionally, it has saved my *** on several occasions, but actually that was long, long ago - I've not really needed its services in many years. Financially, I agree, it's a bit pricey for a one-trick pony....
    – Tetsujin
    Commented Jul 16, 2016 at 18:48
  • Alternatively... assuming everything is nicely backed up - try Sierra & convert to APFS... edit maybe forget that - not sure it's bootable yet
    – Tetsujin
    Commented Jul 16, 2016 at 19:00
  • Yeah I am not sure if its available ether. My regular account is not a developer account, and I think the beta for APFS is only for developers at the moment.
    – BorisKourt
    Commented Jul 16, 2016 at 19:11

1 Answer 1


I would still suspect a problem with the superblock or GUID table.

Personally, I would copy the entire drive to an external drive then boot from the external and erase the internal drive. For this I usually use Carbon Copy Cloner

At that point you should be able to install El Capitan fine and then when asked by the installer you can transfer the applications, setting and users from the external drive into the new system.

  • What would you say are the common causes of this type of problem? I would like to avoid it in the future if possible.
    – BorisKourt
    Commented Jul 18, 2016 at 16:31
  • Who knows. These things just happen sometimes. Commented Jul 19, 2016 at 22:18

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