Unable to unmount DDBoost volume

Hello, I need to unmount ddboost volume because I need to mark it "scan needed" (My DD is almost full and I need to clean it. I used nsrmm to delete obsolete savesets but now need to scan the volume because recovered space was very very small)

But when I trying to unmount there is an error message " Volume mounted on Data Domain disk is idle". I dont see any activity using this device so dont see the reason why I cant unmount it.

NW server version: 8.2.3.7 Windows