There are three means of resolution of the problem. The one and only requirement are that Disk Utility must reside on the drive. The version of the OS X does not matter, by at least must be 10.7, 10.8 and 10.9. Disk Utility can be run from the external drive. Using an external drive or OS X Recovery for the starting up of the Mac from another bootable drive. There are many solutions when the user faces these problems. If the internal drive is causing the issue because the OS X Recovery exists as a partition on the physical disk, unable to modify or unmount the internal drive, then the preference must be given to a network drive or an external drive. The reason for this error is the modification of the boot drive, or it is being used by some other process or application. The error occurs in such situations like formatting Mac as well as partitioning and verification and repairing of Mac disk.

‘ Disk Erase failed with the error: Couldn’t unmount disk.’ The error, which is thrown, is the:ĭisc erase failed couldn’t unmount disc.’ Even the Network deployment tools like Apple’s Netinstall service or the DeployStudio fails, on account of this error. They are unable to erase or partition the drive. The user often experiences a problem, while handling some of the Macs, when they are not allowed to repair permissions or directory in Disk Utility.