The Backup Copy Target tab allows you to add media that can be removed as needed. It is the only location that allows you to remove the media without damage to the backups on the Unitrends. This means it can accept USB, eSATA, Tape, and NAS devices, as long as the hardware and Operating System/Hypervisor supports it.
If the Backup Copy Target device is removed, when you add a new Backup Copy Target device, it has to be prepared, named, and then properly selected in the Backup Job for use to send the data to it. This is a quick, but manual process. You can minimize the amount of work you need to do by using external docking stations, where the controller is presented to the Hypervisor for sharing. This means you do not need to make changes to the UB vm in VMware every time you change a disk.
As you are using a USB Hard Drive, I would recommend using the Add Hardware option and selecting the USB Device. This simplifies the process of assigning the disk to the Unitrends Backup virtual appliance. Once added, you use the Scan For Mediabutton, to detect the drive, then you can Erase it and give it a new name. I recommend a new name every time, so that it is easy to find in the Backup Copy reports. Once it has been made ready, you can edit the Backup Copy Job, and select the new name, then Save the Backup Copy Job.
After adding it to the UB, save the settings and return to the Unitrends appliance. Click on CONFIGURE > Backup Copy Target and click on the Scan For Media button.
Once you see the media, you can create or edit your Backup Copy Job and select it.