This is mostly for design planning. We do not have 10000 hosts but designing for scalability is always important and we do have a need for almost 1000 in the next few years.
Assuming we have:
HA vCloud Directors (quantity of 2)
(this gives us a maximum of 25 vCenter servers
Each vCenter server would have at least 400 hosts
For the management networks, I would not think that it requires each host's management network to be on a local subnet to the vCenter server, but I've seen blogs talking about issues when changing this. Is it best to keep your hosts and vCenter on a local subnet or is it ok to route between the vCenter server and the esxi host? With 400 hosts that sounds like we either need a subnet larger than a class C or route to each host.
If someone smarter than I can help I would greatly appreciate it.