When formatting or partitioning a drive, an error occurs stating the drive cannot be dismounted or unmounted

STOP Critical: The errors described below are not exclusive to Western Digital hard drives and are controlled entirely by your operating system. If the steps below do not solve your issue you will need to contact the publisher of your Operating System (Microsoft or Apple) or your system manufacturer for assistance diagnosing your OS.


When formatting or partitioning a WD internal drive, external drive, or Solid State drive an error occurs stating the drive cannot be dismounted. Depending on your Operating System (OS) the exact wording of this message will vary. These errors can occur on both Windows and Mac OSX.


These errors occur when another program or service is actively using the drive. In most cases this will be something like an Explorer or Finder window, a file transfer to or from the drive, or security software (such as an anti-virus) scanning the drive for problems. Sometimes this can be caused by other devices on your network using the drive (such as another computer, media player, or tablet). In rare cases the drive could be in use by malware, or other hidden software on your machine.


In order to resolve this issue you will need to determine what program or service is using the drive. The steps below will assist you with making this determination. After each step, try to format/partition the drive again:
  1. Close all obviously open programs including explorer and finder windows, web browsers, and documents. Remember if you are on a Mac to close them from the Dock. If you are on a Windows machine make sure nothing is running in the Taskbar.
  2. Reboot your computer and close any programs that launch with your computer.
  3. Boot your computer into Safe Mode (for Windows) or Safe Boot (for Macs).
  4. Scan your system for any malware or other undesirable software.
  5. Temporarily disable any anti-virus and other security software running on your computer. You may need administrative access to do this. Make sure to re-enable it when you have finished following these instructions.
  6. Disable any backup software such as Time Machine and Windows Backup.
  7. Disconnect the ethernet cable from your computer or disable your wireless connection. This will make sure the drive isn't being read by a program running on another computer or device on the network.
  8. Try formatting or partitioning the drive using another USB/FireWire/eSATA cable and on another computer if possible.

In case the answer did not answer your question, you can always visit the WD Community for help from WD users.

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