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Giving up means you have accepted defeat. Or you can run Erase twice the first time will unmount the partition and fail, and the second time will actually do the format (which will succeed). You can manually unmount the partition before running Erase.
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Click the “Erase…” button at the bottom.Select “GUID Partition Map” for “Scheme”.Click on the “Erase” button at the top.On the left-hand pane, select the hard drive (not the partition under it, if any).Click on the “Disk Utility” option and click the “Continue” button on the bottom to launch the “Disk Utility” application.Do the following to format the internal hard drive: When the installer finishes loading, you will see a “macOS Utilities” window appear. Note: Under macOS Sierra, the Erase function will fail if the USB drive’s partition is mounted.(USB 2.0 and large capacity drives will take longer.) After the format completes, the partition will be mounted under “/Volumes/Sierra” (or whatever name you selected above). The format operation may take several minutes to complete.Click the “Erase” button in the warning popup dialog if you get one. Select “Master Boot Record” for “Scheme”.
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Select “Mac OS Extended (Journaled)” for “Format”.Input a name like “Sierra” (this name will be overwritten later).Click on the “Erase” tab (or button at the top).On the left-hand pane, select the USB drive (not the partition under it, if any).Plug the USB flash drive into your Mac.Format the USB flash drive using these steps: