Power outages are not infrequent where I live (something I find quite confounding – to be honest) and earlier this week we had an extended power outage and my Hyper-V servers were powered off uncleanly.  When the power returned I had to sit down and make sure that everything came back correctly.

At first glance – everything looked good.  My Hyper-V servers powered up happily and started up all the virtual machines.  Hyper-V Replica reported that it was in a critical state – but it automatically scheduled resynchronization for all of my virtual machines.  But as I was going through the virtual machines – I found a problem.

Something had gone wrong with my firewall.

I could not figure out what exactly was wrong – but it was using 100% CPU and not allowing any network traffic through.  I shutdown the virtual machine cleanly and restarted it – but no dice.  It still would not work.  Thankfully, there was a simple solution.

I shutdown the misbehaving virtual machine and started up the replica version of it.  This came up with no problems and started functioning correctly – as it had not been powered off uncleanly,  Yay!

Now, there is a key point to make here:  if I had performed a planned failover in Hyper-V (select the primary virtual machine and perform a planned failover) this would not have worked.  Hyper-V would have copied across the outstanding (bad) changes and would have broken my replica virtual machine too.  What I actually did was go straight to the replica virtual machine and selected to perform a failover (not planned).  By doing this, Hyper-V did not copy across the latest data and everything worked.

At the end of this process I reversed the replication relationship and was good to go.

Cheers,
Ben