I looked through much of VMware’s documentation and couldnt find any easy calculation on how to size your database (For 4.1 I did find http://www.vmware.com/support/vsphere4/doc/vsp_4x_db_calculator.xls, but didn’t find anything similar for 5.0). Because of this, I can only assume they are more concerned with you knowing how to change the DB sizing than they are with how big the DB actually is.
There are 2 settings: Statistics Intervals and Database Retention, both of which are managed in the same method.
- Open Virtual Center and connect to a vCenter Server
- On the menu bar, select Administration | vCenter Server Settings
- In the left pane, select Statistics
- Here you can change the Statistics Levels and retention for performance data
- This also allows you to enter the number of hosts and VMs data will be collected from and provides you with an estimated database size
- In the left pane, select Database Retention Policy
- Configure the database to discard historical tasks and events as appropriate
More specifics about these settings can be found on pages 35 and 41 of http://pubs.vmware.com/vsphere-50/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-50-host-management-guide.pdf