What version of Data ONTAP are we referring to here? How many FlexVols do you have presented to Cinder in your environment? How many concurrent snapshots are we talking about here?
Cinder snapshots are implemented as Data ONTAP file or lun clones versus Data ONTAP snapshots. Rapid cloning support for Cinder snapshots is available for both NFS and iSCSI with our Unified Cinder driver. With that being said, performance optimizations in this area have been made in later versions of Data ONTAP, hence my first question above.
With respect on how to setup and utilize portions of the NetApp Unified Cinder driver to work with iSCSI, head over to the Deployment and Operations Guide here for more guidance: