Hyper-V Lessons Learned

The past several weeks have been rather hectic and busy. Between work and studying for my Citrix XenServer certification, there’s been a whole lot going on. Virtualization has long been been a passion of mine in the world of IT, and I am certainly getting hands on with lots of virtualization platforms these days (tis one of the many benefits of working for a managed service provider). I have recently been working on a VMware to Hyper-V migration project and have come across a number of interesting gotchas that I figure would be useful to others going through the same process. Some of these lessons range from NTP with Linux, to troubleshooting cluster connectivity, the migration process itself, and some other fun gotchas.

The Conversion Process Itself

Converting virtual machines from VMware to Hyper-V has become and incredibly simple process. First of all on one of your Hyper-V hosts download and install the Microsoft Virtual Machine Convertor (https://www.microsoft.com/en-us/download/details.aspx?id=42497). Once this is downloaded, there is a simple wizard in which you can choose to do a P2V or V2V conversion to either Azure or Hyper-V. From there it is simply a matter of specifying the hostname of the Hyper-V host that will be the destination for the VM, choosing where to store the virtual disk, as well as whether you want fixed disk or dynamically expanding, and VHD or VHDX. At this point the final step is to put in the information from your vCenter server, choose the VM to migrate (powered off beforehand), and follow the wizard to victory. The mechanism by which the conversion takes place is that VMware will export the virtual machine in OVF format, which will then be copied into the Hyper-V workspace and imported into Hyper-V. It’s actually a fairly slick process, however it is time consuming and there are definitely some gotchas. For one the NICs added during the migration process that replace the VMware virtual adapters will be identified as different interfaces on Windows machines so static IPs will have to be re-entered. This is not the case for Linux, as the interfaces file stores the static IP config and there are no issues I have run into during the conversion process with Linux NICs.

Licensing Your Hyper-V Hosts

If you are a primarily a Windows based shop running 2012 R2, I highly recommend setting your Hyper-V hosts up with Datacenter licensing. The Datacenter license covers up to CPU sockets with unlimited VMs on the same hardware. One of the wonderful features of this is that it allows for AVMA or automatic virtual machine activation. Meaning that instead of activating each VM to MS activation servers, you are actually able to activate them to the VM host with Datacenter licensing. Per the following technet article you can activate using an AVMA key (provided in the article) to activate Datacenter, Standard, and Essentials licenses to the host. https://technet.microsoft.com/en-us/library/dn303421.aspx

The activation syntax must be run from an elevated command prompt with the following syntax:

slmgr /ipk <AVMA key>

For this functionality to work, you will also need to ensure that Data Exchange is enabled in the Integration Services for the VM (this is the default behavior)


NTP Issues For Linux VMs

I learned the hard way after migrating Linux VMs to Hyper-V that one of the default integration services is time synchronization with the host. I had assumed that NTP would override this behavior but I assumed incorrectly. In VMware when you create a VM if you choose a Linux OS profile it actually turns off this time sync behavior, however in Hyper-V there are not OS specific defaults for hardware, so this feature is on by default all the time for all hosts. If the linux host is running Ubuntu 14 or newer, Debian 8, or Centos/RHEL 7 (really anything that uses systemd) you can run the command timedatectl to see if NTP is running and if it is synchronizing. I found that NTP would not sync if time sync was enabled in the integration services for the VM. To avoid countless annoying Nagios emails about NTP drive I simply chose to disable this functionality in the interest of consistent time and less email.

ntp sync no


NTP not synchronized due to time synchronization integration services being enabled.

time sync setting


Uncheck the Time Synchronization Options to corret

ntp sync yes


NTP synchronized switches to yes after making changes to integration services

Converting Windows VMs with Multiple Disks

One of the more obscure things I have discovered with migrating from Vmware to Hyper-V is that windows VMs with multiple disks import both disks properly and both show in the settings for the VM, however in the OS the additional disks are not enabled by default. To remedy this you simply need to go into disk management (diskmgmt.msc) and right click the disk and choose to bring it online. Once this is complete the disks will show properly.

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