After I wrote in a recent blog about snapshots and why they are useful, I had a long conversation with some people about the fact that snapshots should be removed when no longer needed as they can consume large amounts of disk space. I was told that even when administrators had indeed removed their snapshots, the space was not reclaimed. We looked around on their systems, and after digging into it a bit, we saw that they were still running Hyper-V 2008 R2.  I realized then that I had a flawed assumption: that most people had upgraded to Hyper-V 2012 (and soon to Hyper-V 2012 R2), but many have not. In fact, in Hyper-V 2008 R2, the merging of a snapshot into the parent VM will not happen until the VM is turned off, so the space used by the snapshots won’t be available until these VMs are shut off, and they cannot be turned on until the merge is complete.

In a recent post here on our Hyper-V Blog, Maria Pressley provided a number of reasons why users would want to migrate to Hyper-V 2012 R2 .

As seen first-hand, there are so many features that are not available in the older Hyper-V hypervisors, features that make it much more difficult to manage and configure. When managing a Hyper-V system, the most critical resources for VM users are CPU, memory, storage, and networking. The newer versions of Hyper-V are much more flexible in their management of these key resources, as follows:

  • Memory optimization

Users can configure startup memory and minimum memory configurations for their VMs, so that once up and running, the memory can be used for other VMs. This allows for more consolidation, and is particularly useful in virtual desktop environments. Note that you can also prioritize memory availability for a VM based on its weighting.

  • Storage Optimization

In Hyper-V 2012 R2, administrators can resize VHDXs while a VM is up and running. This means the amount of disk size for a VM can be altered without forcing downtime. Note that this feature is not supported for VHDs and that the virtual disk must be attached to a SCSI controller, not to an IDE controller. When shrinking a disk, it can only be reduced to the size currently in use by the VM, i.e., the size of the volume. In order to reduce the size any further, you must first use the Disk Manager within the VM to shrink the volume.

  • CPU Optimization

Resource metering, described in detail in this blog post (Reference this post) allows administrators to track the resources consumed by a VM over time.  This feature is only provided in Hyper-V 2012 and above.


  • Network Infrastructure

Hyper-V 2012 provides the ability to configure PVLANs, which allow Hyper-V administrators to isolate VMs from one another, while allowing them to connect externally to the network. To use this feature you must first configure a VLAN ID for your network, then use the following PowerShell command to put the switch into isolated mode.

With this command, I have isolated VM Windows_7_Lisa to an isolated network with VLAN ID 10, and secondary ID 200, as seen here:

If I want to remove the isolation, I can specify a mode of “Untagged”, as seen here:

You can also set up trunks and other network options as defined at this link.

In summary, if you are still using Hyper-V 2008 R2, you’re not able to use many of these features and many others not even described here, so you should plan on an upgrade as soon as possible.


  1. To upgrade to 2012 or 2012 R2, is it as simple as moving VM’s off to another cluster node, update the host, move vm’s back, upgrade other host, then run some sort of upgrade on the VM’s themselves? Or is it (much) more complicated than that?

    1. Hi, the upgrade process depends on which host OS is being upgraded, Windows Server 2008 R2 with Hyper-V or Hyper-V 2008 R2. For Hyper-V server, the upgrade process as you’ve described — export VMs, reinstall host, import VMs — is a good approach. You do not have to change the VM disks from VHDs to VHDXs, as 2012 will support the older disk format. I found this information to be helpful.

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