OnCommand Performance Manager is the way to go for Clustered Data ONTAP, but it doesn't support 7-mode (you can still use OnCommand Unified Manager Core but the performance graphs are lacking). For realtime (and some historical) graphing, the Graphana/Harvest tool is very nice (and works with both cDOT and 7-mode), albeit a bit harder to configure. Both are free options, just look under your Downloads on the Support site and follow the documentation for installation help. Of course if you have a heterogeneous enviroment with other vendor's storage (EMC, HP, IBM, etc.) or need more advanced data analysis and reporting, OnCommand Insight is great but definitely NOT free.