Hyper-V Replica: New VM replication tool for cost-conscious IT shops

Hyper-V Replica, the new VM replication feature in Microsoft’s next hypervisor, is a free and viable disaster recovery tool for SMBs and enterprises.

The pre-beta version of Hyper-V 3.0 boasts a number of new and improved features, including a virtual machine replication

technology known as Hyper-V Replica. It uses the Hyper-V Volume Shadow Copy Service (VSS) writer to prepare a snapshot of the virtual machine (VM) on the primary host (which can remain active) and moves the data to the secondary host. This capability adds disaster recovery capabilities to Hyper-V 3.0, allowing a virtualization administrator to have cold, ready copies of VMs anywhere in the world. 

Hyper-V Replica creates copies on a VM-by-VM basis. While it is possible to replicate every VM to an alternate host with Hyper-V Replica,  in my experience, the tool is better suited to replicating one-off line-of-business VMs that provide important infrastructure fault tolerance, rather than full virtual environments. As such, Hyper-V Replica may be impractical for large enterprises with hundreds or thousands of VMs. In these situations, administrators can use PowerShell to configure multiple VMs at once.

Even so, Hyper-V Replica provides a free and viable disaster-recovery tool for small to medium-sized businesses or larger organizations that selectively replicate VMs. The potential benefits of replicating part of your virtual environment give this feature a value not found in other free products and brings Hyper-V 3.0 to a new level of maturity.

What you need for Hyper-V Replica
You’ll need the following equipment to replicate VMs in Hyper-V 3.0:

  • A secondary host server with processors from the same family (e.g., Intel Xeon or AMD Opteron) as the primary host. Keeping hosts on the same processor architecture reduces complexity of live migration and failover. In other respects, the secondary host can have different resources than the primary.  For example, the primary server could be a highly available host cluster, and the secondary could be a standalone host with local disks.
  • Enough memory in the secondary host to support the replicated workloads. This is where the Hyper-V Dynamic Memory feature can really shine, maximizing the number of VMs on the secondary host.
  • Enough disk space to hold all of the VMs and potential snapshot versions, as specified in the replication configuration.
  • Sufficient network connectivity and bandwidth between the hosts and end users.

When using Hyper-V Replica, the main goal should be to provide functionality if there’s a major problem with the primary host or data center. To defray costs, you can purchase a different class of hardware for the secondary host. But lower-level wide area network links or host resources may result in slow performance and response times. That said, infrastructure and line-of-business applications will remain available, offsetting the potential losses in productivity.

Hyper-V Replica walkthrough
Here are the basic steps in replicating VMs to another host,  assuming you have a primary host with VMs and a secondary host without VMs. Hyper-V 3.0 is currently in pre-beta, so the process and screen prints below could change.

First, open Hyper-V Manager and add the primary and secondary host servers. Next, right-click on the secondary host and choose Hyper-V Settings.

In the Hyper -V Settings window, choose Replication Configuration and perform the following:

  • Check Enable this computer as a replica server.
  • Check Use Integrated Windows Authentication (HTTP).
  • Choose the storage location for VM files on the secondary host.
  • Click OK.


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Next, right-click on a VM you would like to replicate and choose Enable Replication.


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Then, type in the name of the secondary replica server and the port.


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Keep the default for Virtual Hard Disks, including all VHDs and VHDXs, to replicate unless there are VHDs that you do not want to bring over to the secondary replica host.


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Select the frequency and number of recovery points stored on the secondary replica host. (Note: Full copies of each replica are not stored on the secondary replica host. Only differences are stored on the secondary replica host as AVHDX files.)


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Next, choose when you want to start the replication.


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Verify the summary screen and choose Finish.


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Use the Hyper-V Manager to ensure the VM was replicated on the secondary host, or right-click on the VM and choose View Replication Health.


(Click image for an enlarged view.)

Hyper-V Replica does not scale well to larger enterprises at this time, but it is still simple to configureand provides SMBs with a viable option for improved disaster recovery.

For more information and observations on Hyper-V 3.0, visit VirtuallyAware.com.

This was first published in December 2011

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