Hello Sushant . As Alexander mentioned, you can pair two appliances (hardware or virtual controllers) . Or you can use standalone appliance . In standalone mode you can connect X amount of AP's . In paired mode you still will be able to connect X amount of AP's to each controller , but in case one of the controller is gone (e g lost network connectivity , upgrading , rebooting or failed ) all it's AP's will fail over to the one controller which stays alive . In this case controller will support 2xX (twice) amount of AP's ; there will be no functionality/features lost or anything . Each Extreme Controller designed and tested with the double capacity (in terms of number of AP's , number of connected Clients per controller) in mind for that purpose.
If you pair diffrent types of appliances ,e.g. one controller is C25 which can have 50 AP's and one controller is V2110 which can have 250 AP's , then in case "bigger" appliance fail the "smaller" appliance will take only first 50 AP's due to limitation , therefore it will serve 100 AP (50 locals and 50 foreign) .
