vCenter Server Appliance large scale deployment requirements

For a large scale deployment of vCenter Server Appliance to manage more than 400 hosts or 4000 virtual machines, you must modify the virtual machine settings so that they can meet large scale requirements.

Log into the vCenter Server Appliance administration interface at https://IP address or FQDN of vCenter Server Appliance:5480 and navigate to Services. In the Inventory Size drop-down menu, select large and click Save Settings.

Source:-
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2057376