I recently experienced problems removing a USB drive safely from a Thinkpad T440p running Windows 10.
I saw this warning:
Windows is unable to stop the device 'USB Mass Storage Device'. Don’t remove this device while it is still in use. Close any programs using this device and then remove it.
I checked if I was deliberately using any files or folders on the drive, but that was not the case.
I checked which processes held handles on the D: drive using the useful utility handle.
C:\bin\Handle>handle d:\ Handle v4.0 Copyright (C) 1997-2014 Mark Russinovich Sysinternals - www.sysinternals.com System pid: 4 type: File FA0: D:\$Extend\$RmMetadata\$TxfLog\$TxfLog.blf System pid: 4 type: File 1788: D:\$Extend\$RmMetadata\$TxfLog\$TxfLogContainer00000000000000000002 System pid: 4 type: File 193C: D:\$Extend\$RmMetadata\$TxfLog\$TxfLogContainer00000000000000000001 System pid: 4 type: File 1B60: D:\$Extend\$RmMetadata\$Txf
I found this in Event Viewer:
Log Name: System Source: Microsoft-Windows-Kernel-PnP Event ID: 225 Task Category: (223) Level: Warning User: SYSTEM Description: The application \Device\HarddiskVolume4\Windows\System32\Taskmgr.exe with process id 7432 stopped the removal or ejection for the device USB\VID_1058&PID_1023\57584C3145313145534A5A36.
The problem was solved by closing task manager. Then the USB drive could be removed safely.