Ask Different is a question and answer site for power users of Apple hardware and software. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

When I try to install Mac OS X there is no partition for me to choose. I tried to create a partition and got the error, "Partition failed with the error: Couldn't unmount disc."

Anyone have a clue? I can't install any OS unless I am able to create a partition.

share|improve this question

How are you doing this? What are you booted to? You can not partition a drive which you are running.

Try inserting the install DVD which came with your computer and see if you can repartition or erase that way. If you still get the error message, select the drive you want to erase on the right side and then in the top toolbox select 'Eject'. If it ejects, rock on. Otherwise you might have an issue where the drive is damaged and can not be unmounted as the active OS is attempting to read the Volume Header and getting an error kicked backed.

share|improve this answer

"Andrew U" has it right. Sounds like the disk is active (mounted).

Reboot the Mac force the Mac to boot from the DVD and start a new install.

If the disk you are installing on already had data and partitions, either choose the Erase and Install method or do it manually by using Disk Utility from the Utilities menu in the Installer.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.