Partition Failed error If you have attempted to partition a drive from Mac OS X and received a “Partition failed” message with the error “Couldn’t modify partition map because file system verification failed.” you can fix the problem with the file system check command line utility. To do this properly, you’ll need to boot into Single User Mode as well:
    1. Reboot the Mac into Single User Mode by holding Command+S during boot
    2. At the command prompt, type:
/sbin/fsck -fy
  1. When fsck is complete, type “exit” or “reboot” to reboot
  2. Boot the Mac as usual, verify the disk again in Disk Utility, and partition as usual
Boot the Mac as usual and relaunch Disk Utility to verify the disk. Go ahead and partition the drive as usual, this time without any such error message. I have encountered this error a few times when partitioning the boot drive from OS X Lion, most recently after a clean installation when setting up dual boot for OS X Lion and Mountain Lion. The cause of this remains to be seen, and repairing the disk from Disk Utility itself doesn’t work, even when in Single User Mode or when booting from another drive.

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