If WHS is detecting the trigger of 10GB(?) free space, the network healty will change from green into a different colour.
At this time WHS should immediately stop all further planned backup actions due to the chance that the admin is not able to add new drives or making some free space - let's say the responsible is off duty for a while. This implies to stop the possebility to add files to the shares to.
Without an intelligent logical management there will be more trouble than advantages. What is WHS during a worst case scenario "out of space". Which actions will be deactivated?
We are talking about securing the already accomplish backups and duplicated shares (if configured). Which should have maximum priority to all other activities? My wish: securing, securing and securing.