Here's our scenario:
Site 1 has 3 hosts, and our vCenter server is here.
Site 2 has 3 hosts.
All hosts are ESXi 4.1 update 1.
If I view the Performance tab for any host in Site 1, I can view realtime, 1 Day, etc., i.e. all the views give me graph data.
For the hosts in Site 2, I can view the realtime graphs, 1 Day and 1 Week both say "No data available". 1 Month had mostly nothing, 1 Year shows that it was working fine for a long time and then started breaking.
1 Month view:
1 Year view:
What would cause this loss of performance data?