Is there any reason why adding a host to an active DRS cluster that has say 20 running VMs on it would cause issues? I understand a host should be in maintenance mode when adding or remvoing from a DRS cluster, but this can be done by disconnecting/removing/adding the host to the cluster. Is there a technical reason why it shouldnt be done? Does it disrupt DRS or HA?
you will be fine. Best practice dictates to enter and leave a cluster in maintenance mode, but....
you will be fine. Best practice dictates to enter and leave a cluster in maintenance mode, but....