If you are attempting to unmount or eject an external drive, and the drive is failing to unmount, that is usually an indication that a file on that device is in use by another application.
To determine what files are being accessed on a drive that are preventing you from unmounting, follow these steps:
Select the drive from the left of the Drive Genius Window that you’d like to check, then select the ‘Active Files’ utility in the Protect section of the feature window.
Press the ‘Start’ button. Drive Genius will notify you of any files that are currently actively being accessed from the drive. If there are no files being accessed, the check should complete successfully, otherwise it will report those files.