I have a fully licensed ESXi 6.5 VM host that has 3 VMs running. I am trying to add it to a new Cluster (HA, EVC, DRS off) that I have created on a vCenter 6.7 Update 1 VCSA, but it tells me the host needs to go into Maintenance mode before it can be moved? I always thought it was possible to add a host with powered on VMs to a cluster?

I tried adding it to the Datacenter instead of cluster, and there is no mention of the need to be powered off.

Also, the option when right-clicking the Cluster is Add Hosts... but on the datacenter it is Add Host...

I recently rebuilt this VCSA from scratch as it was a Windows vCenter that horribly broke (VMware Support unable to resolve issues). Adding the hosts from the old vCenter to the new one, was no problem.


TL;DR: use the Flex/Flash client

(Had to open a ticket with VMware to find this out.)

So here's the deal - even though the HTML5 client is marketed in vSphere 6.7 as being an almost complete functional equivalent of the Flex/Flash client, there are still multiple areas where there are differences.

One area is when setting up vCenter HA - our HTML5 client wouldn't work at all, but if it did work you'd still only get the Basic setup workflow instead of choosing between the Basic and Advanced setup workflows that are available in the Flex/Flash client.

The other area is where your and my issue came in - that of adding hosts to vCenter 6.7. Apparently the HTML5 client requires the host to be in Maintenance Mode, whereas the Flex/Flash client does not. No idea why, but shrug there you go.

Hope that helps!

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  • +1. Just had to download flash after years. I'd like to add that it still happens with vSphere 6.7U3b (current as of 2020/02/04) and despite the ESXi host version (I have a 6.7U3b build 15160138 and a 14320388 and both do as well), so not necessarily 6.5 host Vs 6.7 vCenter, as in the OP. With the Flash client my hosts were added without going in maintenance mode. – Marco Feb 4 at 22:08

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