Windows Server 2012 New Feature: Hyper-V Replica for Failover

For mission critical systems, we often want to try to achieve the highest level of up time as possible, and the best disaster recovery strategy.  Often this involves expensive software which replicates servers or data for failover purposes.  This means that if a primary server goes down, another server is waiting to take its place.  Sometimes this failover is automatic and sometimes a network admin has to flip a virtual switch to make the failover go live.  In all cases, the solution requires lots of expensive licensing and extensive planning.

Hyper-V is Microsoft’s hypervisor platform for virtualization and is part of Windows Server 2012 Server (Standard and Datacenter editions), as well as Windows 8.  There is no extra cost for using Hyper-V, only the license for the copy of Windows it is running on.  Microsoft also offers a completely free option as well in Hyper-V Server (which is Hyper-V as an operating system without Windows).

Hyper-V Transports Logs to Replica (click to enlarge)

Hyper-V Transports Logs to Replica (click to enlarge)

In Hyper-V for Windows 2012 and Hyper-V Server, we now have a built-in replication feature.  This means that you can configure a virtual machine running in Hyper-V to automatically replicate (as often as every 30 minutes) to another Hyper-V host.  If the other Hyper-V host is on a different network or even a different site, you can set a different IP configuration for the failover server.

Creating The Replica

First you create your replica starting point which is basically a copy of your entire virtual machine.  During this process you also configure where the VM will replicate to (the recipient Hyper-V host).  The initial bits can be quite large, so Microsoft gives us a few ways to transport this large amount of data to the recipient host including using an external USB drive.

Once the initial bits are copied over to this second Hyper-V host, then replication starts at the interval you specify.  With Hyper-V Replica only one of the copies of the VM is running at any given time.  Changes are merged into the replica VM similar to the way Hyper-V merges snapshots into a stopped VM.

Failing Over to the Replica

Using Hyper-V Manager there is no way to create an automatic failover, so this part is manual.  To failover, simply right-click on the main VM, and select “Failover”.  The primary VM turns off and the replica turns on.  There is even a feature to do a test failover.

Not bad functionality for a free product!!  To see how Hyper-V stacks up against VMware, check out this episode of ITProGuru vs. Radio.


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