Resolving unmount disk issue from USB drive. For this you can follow these steps which are mentioned below.
So in order to overcome from this problem one can try to boot the system from the other drive thereafter running disk utility in it. According to experts advice when there is modification done in boot drive which result as partition failed could not unmount disk error. Typically this type of error appear while partitioning, repairing or verifying disk permission and formatting of disk using disk utility which would prevent you for doing all these tasks.
Definitely it is quite hard time for you whenever partition failed could not unmount disk come across.
