Hello theire,
i have same config with several Clusters as i create Clusters per CPU Architecture. Westmere,ivy,Sandy,Haswell. i don't use EVC.
Hm wouldn't sense now an Kind of Problem. 1 Point is that theire is additional Heartbeat through storage per Cluster. But on other Side theire is more less overhead for HA Master/Slave per Cluster .
For overally optimize, maybe have a look if you have latest Supported Firmware on Storage Boxes. CHeck if theire is support for Alua/RR and that you use ATS/SCSI Reservation instead of nativ SCSI Reseration. If you fully have ATS Support, you could upgrade to have ATS-Only nativ .
Best regards
Max