Explorer.exe and System prevent the ejection of an external hard drive

I have an external hard drive that I could not eject despite all programs being closed.

I followed the instructions explained in this answer to check which process was preventing the drive from being ejected.

I found two entries in the log:

  • The application DeviceHarddiskVolume5Windowsexplorer.exe with process id 21776 stopped the removal or ejection for the device USBVID_0480&PID_090120211220017702F.
  • The application System with process id 4 stopped the removal or ejection for the device USBVID_0480&PID_090120211220017702F.

What should I do? Should I kill explorer.exe? What is System? Should I kill that too?