Hi CloudMiner, you can use OCUM - no additional license needed if you have cDOT. If you have 7-Mode you can ask for a free license - to monitor and warn you by e-mail when the volume and aggregate reach a defined percentage of utilization.
You can use the autogrow feature on volume if you want to automatically provision more volume space in case of needed (this way you need to monitore your aggregate only)
You can use the Snap AutoDelete feature to free up your volume if it becomes without space.
The OnCommand Insight is bigger than that , it will be helpful on monitoring your entire environment, virtual machines, physical hosts, SAN Switches and Storage.