How to "safely eject" a USB hard drive from ShareSpace after backup completes?

I backed up my ShareSpace NAS to a 2 TB external HD.  When the backup completed, I unplugged the USB cable from the NAS and then received an alert that the USB drive had been “unsafely removed.”  Nowhere in the NAS documentation does it mention how to “eject” a USB drive safely!  I’m storing the backup drive in another physical location for safety so leaving it connected is not an option.  Any suggestions?  I tried ssh’ing into the NAS and umounting the USB drive first but still recieved the “unsafely removed” alert.

Answering my own question – in the “Advanced Mode”, “Storage”, “USB SHares”, there is a small icon to the right of a mounted USB drive that “removes it safely.”  Would have been nice to put that in the Users Manual, or did I just miss it?