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When your computer finishes starting up, choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.If you're using an older version of OS X and your computer came with a Mac OS X Install disc, insert the installation disc and restart the computer while holding the C key instead. If you're using OS X Lion or later, start the computer from Recovery System or Internet Recovery.
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Use these steps to use the Disk Utility app to verify or repair a disk. Resolve startup issues and perform disk maintenance with Disk Utility and fsck You may also want to use Disk Utility from Recovery if the previous steps don't work: Using Disk Utility to verify or repair disks - Apple Support If you have any files open from this volume, it is best to restart your Mac and attempt the same process again. I understand that you're receiving an error within Disk Utility while attempting to repair the volume. Thanks for visiting Apple Support Communities!
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