I am struggling to understand why the default option for failover and "failover plans" is to bring up the replica servers without shutting down the source hosts - please can someone help me better my understanding of this?
It seems to me that one would never want to do this, as the replica and the source machines would divert in state from each other immediately they are started. Further, even if this was just for testing that the replica was actually boot-able, then the very action of bringing it up by means of the failover will either cause an IP clash and hence end users could be accessing both the source and replica machines concurrently, or if a Re-IP rule is configured for the replicated VM then a DNS issue will occur where the Re-IP address will overwrite the source address in DNS and get replicated around the Domain, causing end users to no longer be able to access the source host. I would also be a bit concerned with two identical machines being active on the Domain at the same time that might possibly cause corruption in AD.
It seems to me that one would only ever want to be able to do a "planned failover" that stops and fails over the source host (with latest changes or not) followed by either an "undo failover" (to revert back to source losing replica changes) or a "planned failback" (to bring replica changes back to source).
What am I missing here? Why is this even an option, let alone the default one?
Thanks in advance