Linked Mode was first intoducedd in vSphere 4.x and it has come a long way with vSphere 6.0.
Enhanced linked mode (ELM) allows administrators to manage multiple vCenter servers from one place using vSphere Web client. vCenter servers in ELM can replicate roles, permissions, licenses and policies between them.
ELM also enables Cross vCenter vMotion i.e you can migrate virtual machines across clusters on separate vCenter instances; subject to network limitations.
Previously linked mode configuration was only possible with Windows based VC as ADAM was used as the replication engine between the VC’s.
ELM in vSphere 6.0 don’t rely on ADAM anymore but have its own replication system which is a multi-master replication technology also called VMDir based on Open LDAP which means replication now works across Windows vCenter as well as vCenter appliances.
Note: All vCenters configured in ELM can be managed only from Web Client. If you are using vSphere C# client then you can only manage that vCenter server to which you are connected.
There are 2 deployment models available for configuring linked mode.
Enhanced Linked Mode with an External PSC Without HA
In this mode you have an external PSC and your first vCenter server is linked to this PSC. You deploy additional vCenter server pointing it to the existing PSC and this provides you the Enhanced Linked mode functionality
Enhanced Linked Mode with an External PSC in an HA Configuration
In this deployment mode you have 2 or more PSC’s deployed and configured and they are behind a load balancer to provide HA for the configuration. The vCenter Servers are then joined to that domain using the shared load balancer IP address, providing Enhanced Linked mode functionality that is fault-tolerant.
Graphic thanks to www.penguinpunk.net
To learn more about how to configure HA for PSC’s I would recommend reading this article by Mariusz Kaczorek.
Also please see VMware KB-2113315 for more info.
In my lab setup I do not have any load balancer so I am going to demonstrate the first deployment model.
Apart from core infrastructure components like AD/DNS/NTP/Management Cluster etc I have following in my lab:
- I have one external PSC deployed (psc04.alex.local).
- One vCenter server (vcentersrv02.alex.local) pointing to PSC04.
Now I am going to deploy an additional vCenter Server (vcentersrv03.alex.local) and I will add it to same SSO domain (alex.lab) in which my existing PSC/vCenter server are.
I am not covering all steps of vCenter deployment as its very straight forward and including just that part where I pointed my vCenter server to an existing PSC.
Post deployment, installer will ask you to login to newly deployed VC with user administrator@SSO-Domain
Login to the VC and go to vCenter Inventory list and you will see both your vCenter visible there.
Verify all nodes are green and happy.
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