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The “Replica Replica” in Hyper-V

The “Replica Replica” in Hyper-V

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In today’s article in the “Why Windows Server 2012 R2” series, I’d like to show off a new feature in Hyper-V; something I like to call the “Replica Replica”.

“Huh?”

ReplicationAs many of you know, Microsoft introduced a new, powerful tool for your disaster recover (DR) tool belt called Hyper-V Replica back in Windows Server 2012 Hyper-V and Hyper-V Server 2012.  For those of you who are not yet familiar with it, a Hyper-V Replica is an easily created and up-to-date offline copy of a virtual machine.  On some other host – either in your local or in some remote datacenter – you have a copy of a virtual machine that can be available in case of disaster.  If something bad happens to the production machine, you can failover to the replica virtual machine very quickly. 

For a most-excellent description of Hyper-V Replica is and how to set it up in Hyper-V in Windows Server 2012 Hyper-V, check out this blog post from the series “31 Days of our Favorite Things” -

Windows Server 2012 and Hyper-V Replica (Part 5 of 31) 

“So, what’s new in R2?  What’s this ‘Replica Replica’ you talk about?”

We’ve added the ability to create yet another replica.  It’s a replica of the replica.  It’s an additional offline copy of a virtual machine and its configuration, made available, synchronized and automatically kept up-to-date on yet another Hyper-V host.  Interestingly the request was from our many hosting providers, and it makes a great deal of sense in their scenario, where they are the ones hosting a replica on behalf of their customers.  It only makes sense that they would love to have a backup of the replica they’re hosting.. so why not make it a replica of the replica?

“Brilliant!”

Yeah, I thought so, too.

“How does it work?”

It’s very simple.  After you’ve created the first replica, you right-click on the replica machine and select “Extend Replication…”.  In my example, I have already set up a replica of my domain controller, and I’m going to extend the replication and put a replica of the replica on my Hyper-V Server named HVSR2-1

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The wizard looks and works very much like setting up the initial replication does.  Once you get past the Before You Begin screen…

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…you choose or browse to the server you want to put the replica on (the Replica server)…

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You pick the type of authentication you want to use (based on what has been enabled in the Replication Settings on the Hyper-V Host settings)…

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You pick a replication frequency. 

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NOTICE that I have two choices here, because I had selected the primary replica as sending changes every 5 minutes.  Your choices will depend upon what you selected for the first replica frequency. 

You may not know this (yet), but Hyper-V Replica in Server 2012 R2 allows for more than just the 5 minute intervals that were in the original Hyper-V Replica in Server 2012.  You can have replication send changes every 30 seconds, 5 minutes, or 15 minutes for the first replica.  For the extended replica, you must replicate at an interval that is less-or-equally-frequent to the first replica; with the exception being that you cannot replicate the to the extended replica at the 30 second interval. 

Here’s a quick chart that shows the extended replication interval options available based on the first replica interval selected:

Primary Replica interval selected Extended Replica intervals available
30 seconds 5 minutes
15 minutes
5 minutes 5 minutes
15 minutes
15 minutes 15 minutes

Getting back to our wizard; now we select how many recovery points we want to maintain of the extended replica…

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We select an initial replication method, plus when to launch the initial replication if requested…

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Check the summary…

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And Finish.  We’re done.  And the first extended replication is now going over the wire.

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Pretty cool, huh?

“Pretty cool.  So now I can failover to either of my two replicas?”

That’s right!

Now, if I right-click on the first replica…

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I see that I have similar options to what I had back in Hyper-V 2012.  But now I have an additional “Pause Extended Replication” option as well. 

Here’s a failover scenario for you…

Let’s say I have a virtual machine “DukeN” running on Host A, with replica on Host B and extended replica on Host C.

Host A goes down.  So I right-click on the “DukeN” machine and select Failover…, and DukeN fires up and is now running on Host B.

If I right click the newly running VM and look at the Replication options I have now on the failover machine, it’s pretty interesting…

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I can “Reverse Replication”, which means I can now treat this running (but still considered a replica) machine as the primary machine, and begin replication back to what was the primary location.  Note: if you do this, it essential "orphans” the old extended replica.  You’ll have to re-extend the replication if you want to.

I can “Remove Recovery Points..”, which does cleanup of this replica of any other points still saved.

I can “Cancel Failover”, which will shut this replica down and assumes that the original machine is now available and can be started.

I can “Resume Extended Replication”.  This one is interesting to me.  It assumes that Host C (containing the extended replica) is still available.  When selected from Host B, then Host B becomes the main VM and the copy on Host C becomes the first replica.  Once a synchronization process is completed, you can then go to the VM on Host C and Extend Replication to another host (Host D?). 

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Good stuff?  Try it out yourself by downloading the evaluations of either Windows Server 2012 R2 or Hyper-V Server 2012 R2.  And let me know if you have any comments or questions by posting them in the comments section.

  • Dear Kevin,

    Can we force the Replica to use a dedicated network between two hyper-v hosts?

    I have two adapters teamed together, the virtual switch is created on top as converged network (MangementOS, LiveMigratrion, etc...)

    Each network with a specific VLAN to isolate the traffic.

    The two Hyper-V boxes are in the same LAN.

    Thank you.

  • Hi Sharbel,

    It is do-able, but involves the Hyper-V Replica Broker for a cluster, certificates, and adding entries to the HOSTS file to resolve DNS to use that special network at the proper time.  Check out Chris Crampton's blog post on how to do this: chriscrampton.blogspot.com/.../hyper-v-replica-over-dedicated-network.html

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