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Disconnecting USB Devices from a Virtual Machine
Before unplugging a USB device or using the VM > Removable Devices menu to disconnect it from a virtual machine, be sure it is in a safe state.
You should follow the procedures the device manufacturer specifies for unplugging the device from a physical computer. This is true whether you are physically unplugging it, moving it from host to virtual machine, moving it between virtual machines or moving it from virtual machine to host.
This is particularly important with data storage devices (a Zip drive, for example). If you move a data storage device too soon after saving a file and the operating system has not actually written the data to the disk, you can lose data.