I've currently got a pair of vSphere5 standard servers (physical, not VAs) managing about a hundred ESX 4.1 and 5 hosts in two different physical and logical datacenters. With our last purchase, we bought another vSphere license for the new vS server. I unmanaged all the ESX servers in one datacenter and added them to new vSphere server.
Our previous single-vS-server layout used to be:
-vSphere1
--Datacenter1 (where the physical ESX host was located)
---Folder
----ESX server1
--Datacenter2
---Folder
----ESX server2
Now it looks like
-vSphere1
--Datacenter1
---Folder
----ESX server1
-vSphere2 (new vSphere server)
--Datacenter2
---Folder
----ESX server2
ESX server2 was removed from vSphere1's inventory and added to vSphere2's, so it is now managed by vSphere2.
This is nice and all, as no vSphere <--> ESX management traffic leaves the physical datacenter, except for one huge oversight: when I go to clone a VM, the opposite vSphere server (and thus other datacenter) does not show up in the list on the first page of the wizard.
Is this a bug, a license limitation, or is it just simply not possible to clone a VM from an ESX box managed by one vS server to another ESX box managed by a /different/ vS server?
Linked mode just allows for management of multiple vCenter servers with a single management client - there's no special link created between the vCenter systems for the purposes of moving VMs between hosts managed by each of them.
Do you have any storage that's shared between both data centers, or can you create some (an NFS share, perhaps)? Cloning to there, then an unregister from one vCenter and a register on the other, is a decent workaround.