An architect proposes four 7210 Mobility Controllers (MCs) to support about 1,500 client APs.

The Aruba Mobility Master (MM) hardware appliances are designed to manage large-scale networks. The MM-HW-10K model is capable of managing up to 10,000 devices, which would be sufficient for the customer’s requirement of supporting about 1,500 client APs and a maximum of about 20,000 wireless clients1. Two MM-HW-10K appliances would allow for an active and standby deployment, providing redundancy and ensuring network reliability2.

References:

System Requirements - Aruba

Mobility Master Hardware Appliance - Aruba