Steps to Resolve a Format or Partition Drive Error Cannot Dismount or Unmount Windows and macOS

Description

The drive cannot mount or unmount on Windows or macOS.
Something is using the drive.

Resolution

Find out what is using the drive.
Try to format the drive again after each step.

1. Close all open programs.
   This include files, documents, software, Windows Explorer and macOS Finder.
   Make sure to close them from macOS Dock.
   Make sure nothing is running in the Windows Task Bar.


2. Reboot.
   Close all programs that start on boot.


3. Boot into Windows Safe Mode or macOS Safe Boot.


4. Scan for virus and malware.


5. Temporarily turn off any anti-virus and security software.


6. Pause or turn off all backup software.


7. Remove the ethernet cable from your computer or turn off WiFI.
   This will make sure the drive is not being used by something on the network.


8. Formatting or partition the drive using a different data cable.
   Try a different computer.