Hard drive formatting problem

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Hard drive formatting problem

Hi there,

I've been stupid and I'm looking for some advice. What happened was I went and tried to install Windows 8.1 on my iMac, had a problem with the installation process and whilst in the Windows installer, I ended up screwing up a partition which has ended up as free space which OSX disk utility won't let me format, delete or repartition. It won't work either from within Mavericks or when booted from either a recovery disk or a USB drive Mavericks installer. I've got everything backed up so a complete hard drive format is fine, in fact I already tried that, so starting from scratch might be easiest. If anybody has any ideas how I could fix this I'd be grateful.

At the moment the drive is showing four partitions, Macintosh HD is 2.5TB OS Extended (Journaled), disk1s4 is 314.6MB OS Extended (Journaled), disk1s6 is 134.2MB OS Extended (Journaled) and Free Space is 499.98GB Free Space.

Macintosh HD is working fine.

disk1s4 I'm unable to delete, merge or reformat.

disk1s6 is between a rock and a hard place, because...

Free Space is just flat out unusable.

System is 27" iMac 3.5GHz Core i7, 16GB 1600 MHz DDR3, 3.12TB Fusion Drive

Any help would be appreciated, I'll try not to screw up this time...

Thanks,

Kev

iMac (27-inch, Late 2013), OS X Mavericks (10.9.4)

Posted on Aug 4, 2014 5:06 PM

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Answer 1

Brett L

Community Specialist

Aug 7, 2014 12:45 PM in response to malevolus

Hi malevolus,

It looks like the partition map of your iMac’s fusion drive is corrupted. Fortunately since you have a backup of everything, we don’t have to worry about data loss. Reformatting of a fusion drive does require some special steps though. See this article -

Mac mini (Late 2012), iMac (Late 2012 and later): About Fusion Drive

http://support.apple.com/kb/HT5446

In Particular -

Troubleshooting

The version of Disk Utility that comes with Fusion Drive is unique. Earlier versions of Disk Utility can't be used with a Fusion Drive.

If your system will not start because you see a flashing question mark or another alert:

Press the Power button and hold it down to power off your system.

Press the Power button again. After you hear the startup chime, press and hold Command-Option-R to start up to the Internet version of Mountain Lion Recovery.

A globe should appear with a "Starting Internet Recovery" message. It is now OK to release Command-Option-R.

A progress bar should appear and Internet Recovery should start and ask you to select a language.

Once you select a language, click Disk Utility in the window that appears and then click Continue.

If your Fusion Drive can be fixed with Disk Utility, you'll see a Disk icon with red lettering. Click the disk icon.

A dialog box appears offering to fix the Fusion Drive (shown above). Caution: Clicking Fix will erase your Fusion Drive. If you have a Time Machine backup of your Fusion Drive Mac, see Mac 101: Time Machine for information on how to restore from a Time Machine backup once the drive has been erased.

8. After the process is complete, the volume will change color to black. Quit Disk Utility, click Install Mac OS X, then click Continue to reinstall OS X Mountain Lion.

Thanks for using Apple Support Communities.

Best,

Brett L

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