There are several places to get performance metrics and each would depend on what you 'need' and what the issue is....
1.) Monitoring - available for free in Cloud Manager (but will deploy an EC2 instance). This will give you 3 columns showing each volume, it's IOP count, throughput and latency in sortable columns.
2.) System Manager - one-click access to this from Cloud Manager (3-bar menu, 'advanced', scroll down to "System Manager"). This will also give you high level performance metrics for volumes or SVM's under the Storage tab and by clicking on the name of the volume you want to look at.
3.) Active IQ - free tool that gives some high level information about performance (and great general information about what you use with NetApp). aiq.netapp.com. Ex. You can get information in the "Performance" tab for the cluster, nodes, aggregates and volumes (notice there are additional tabs in the performance window). You can see things like IOPS, throughput and latency over time (up to 2 months). Here you can at least see at a high level if any volumes are highly latent but be sure they are actually doing 'real' throughput.
4.) Unified Manager - this is also a free tool that will give a bit more granular information but needs to be installed somewhere in your infrastructure that has connectivity to the CVO's you want to analyze. Info and downloads available here (requires a support site account) https://mysupport.netapp.com/site/products/all/details/activeiq-unified-manager/downloads-tab
There are more in depth ways to do this and I agree that a Support case could be a good option if you need to go deeper than the above. The most important thing in any performance scenario are to understand the following:
#1 A known problematic timeframe (exact time). Logs or screenshots can be helpful. Performance is a point-in-time concept so this is critical to understand.
#2 A detailed description of what is occurring at the time. i.e Restore operation that normally takes 5 minutes is taking 45 minutes. Latency that is normally x is now y.
#3 How the issue maps to NetApp (volume name in question at the very least)
#4 Performance data DURING the time of the issue (quantifiable things like latency, iops, throughput to start with)