I downloaded and ran the Mountain Lion Installer today for my mid-2007 iMac. After rebooting and preparing to install, I receive an error message that the hard disk was damaged and the installer could not run.

I can't boot to the partition and am working from the install partition instead. Disk Utility cannot repair the partition, and detects no problems with parent volume. Time Machine cannot restore to the partition as it is apparently locked or unavailable (it is greyed out in the program).

I've booted in Single User mode and run /sbin/fsck -fy and /sbin/mount -uw /, but this does not allow me to run fsck on the problem volume - just the install partition it appears.

This is the partition info from diskutil info /dev/disk0s2:

Device Identifier:        disk0s2
   Device Node:              /dev/disk0s2
   Part of Whole:            disk0
   Device / Media Name:      WD Black Caviar

   Volume Name:              WD Black Caviar
   Escaped with Unicode:     WD%FF%FE%20%00Black%FF%FE%20%00Caviar

   Mounted:                  Yes
   Mount Point:              /Volumes/WD Black Caviar
   Escaped with Unicode:     /Volumes/WD%FF%FE%20%00Black%FF%FE%20%00Caviar

   File System Personality:  HFS+
   Type (Bundle):            hfs
   Name (User Visible):      Mac OS Extended
   Owners:                   Enabled

   Partition Type:           Apple_HFS
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 SATA
   SMART Status:             Verified
   Volume UUID:              8880D8D2-AEC8-3466-81D3-4ABBE296733A

   Total Size:               1.3 TB (1278311751680 Bytes) (exactly 2496702640 512-Byte-Blocks)
   Volume Free Space:        817.2 GB (817164238848 Bytes) (exactly 1596023904 512-Byte-Blocks)
   Device Block Size:        512 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Yes
   Ejectable:                No

   Whole:                    No
   Internal:                 Yes
   Solid State:              No


How can I regain write access to the partition to diagnose it?


2 Answers 2


To fix this I re-partitioned the volume from Disk Utility running off a USB boot volume. This got the volume accessible and responsive again. Then I restored from an earlier Time Machine backup, and proceeded to re-download and run the Mountain Lion installer, this time with no problems.

While it may be faulty hardware somewhere, I can't rule out that a bug or some other interference for the Mountain Lion installer damaged the partition. It has been working fine for days now, and was working fine prior to ML.


Please "burn" ML to USB or DVD and boot by it. Then use Disk Utility to repair the disk (or partition). It may be a cable HDD problem, or the HDD is bad.

  • Thanks. I copied InstallESD.dmg to a USB drive and ran Disk Utility from there. It cannot repair the partition, and recommends I reformat it. What exactly is a cable HDD problem? The cable connecting the HDD to the controller may be bad?
    – wxs
    Commented Aug 11, 2012 at 15:44
  • If Disk Utilities can't help you in this problem, please go to Genuine Apple. Replace cable/hdd (or both).
    – tquang
    Commented Aug 12, 2012 at 15:00

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