Hi,
Performance Advisor is a suitable tool to use to verify the performance of the 7-Mode Netapp systesm.
You can also use Graphana -> This is a free based tool.
You can also run CLI Based commands like "sysstat" to check the performance of Netapp.
As you mentioned it's only 1 particular vFiler, then i would be interested on how the vfiler is configured (NFS/CIFS Options, vlan configuration, ports used for vlan etc..)
Hope this helps.
BR
Raj