Symptom
An alert with this message appears in Disk Utility:
"Unmount Failed The disk 'Macintosh HD' failed to unmount because it is in use. The operation has been canceled."
Solution
This is expected behavior for NetBoot clients. You may use all features of Disk Utility while started up from any of the following:
- A Network Install image
- An installation CD
- Another volume with Mac OS X installed on it