Configuring Hyper-V Replica
Once the Hyper-V hosts are configured to enable the Hyper-V Replica capability, the
next step is enabling virtual machines to be replicated. To show how to enable
replication, I will initially use Hyper-V Manager, although PowerShell can also be used
and would be used in any kind of automated bulk configuration. You select the virtual
machine on which you want to enable replication and select the Enable Replication
action. The Replication Configuration Wizard then launches. Then follow these steps:
1 . Specify the replica server that will host the replica and be sure that the
authentication type to use is selected. A check is performed against the replica
server to check the types of authentication that are supported. If both Kerberos
and certificate-based authentication are supported on the target replica server and
are usable, you will need to select the authentication method to use, typically
Kerberos. Additionally, you can select whether the data sent over the network
should be compressed, which will save network bandwidth but will also use
additional CPU cycles both on the primary and replica Hyper-V servers. The option
to use compression is enabled by default.
2 . Select the virtual hard disks that should be replicated. If a virtual machine has
multiple virtual hard disks, the hard disks to be replicated can be selected to
ensure that only the required ones are replicated. For example, you could do this in
order not to replicate VHDs containing just a pagefile, although this does cause
more management overhead and, given the churn of pagefiles, is typically quite
light; so, this is not a mandatory step. Be aware that only VHDs can be replicated;
if a virtual machine uses pass-through disks, they cannot be replicated with Hyper-
V Replica (another reason to avoid pass-through disks).
3 . Identify the frequency of replication, which can be 30 seconds, 5 minutes, or 15
minutes. This step was not present in Windows Server 2012, which supported a 5-
minute replication frequency only.
4 . Configure the recovery history. By default, the replica will have a single recovery
point: the latest replication state. For an extended recovery history, set optional
additional hourly recovery points, as shown in Figure 8.2. The additional recovery
points are manifested as snapshots on the virtual machine that is created on the
replica server; you can choose a specific recovery point by selecting the desired
snapshot. Windows Server 2012 R2 increased the number of hourly recovery
points from 16 to 24, which provides the ability to have a full day of incremental
protection. Windows Server 2012 R2 also improves the mechanics of how the
replica works, which now behaves more like a copy-on-write backup because writes
written to the replica VHD have the replaced blocks now written to undo logs. This
provides performance improvements and continues in Windows Server 2016.