You all know the religious argument: whether you should run vCenter in a VM or not. We’ve discussed in the past some of the pros and cons of doing so. Today I was running thru the KB digest from the guys in the knowledge base department and came across an interesting scenario I had not thought of yet:
How do you enable EVC (Enhanced vMotion Compatibility) in a cluster that is running vCenter? On vCenter4, as long as the CPU baseline does not change from what the CPUs are running at currently, you should be able to do this while vCenter is running. But what if your on 3.5 (which requires all VMs to be down to enable EVC) or if you need to change the baseline from the current when you enable EVC (which also requires the VMs to be down)?
Yes it can be done (if you have enough hosts). All the details can be found in KB article 1013111. It becomes a “shell game” of moving hosts and VMs. You basically start a new cluster with no hosts. Turn on EVC on the new cluster. Put one of your hosts into maintenance mode and remove it from it’s current cluster. You can then add that host to the new cluster. Then you can shut down vCenter and remove it from the inventory (note the storage location) and re-add it into the new cluster and power it on. You can then balance moving VMs to the new cluster. This may be able to be done live, unless the baselines are off which will require the VMs to be cold-migrated. As hosts are emptied of VMs, you can then migrate them to the new cluster.
I don’t believe this should be a major impact on whether to run vCenter in a VM, just one thing to remember if you do.
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