Moving from one platform to another is pretty common these days, but how do you move your virtual desktops? The difficulty of a VDI migration largely depends on which hypervisor you're converting to.
More on virtualization platform conversions
How to streamline multi-hypervisor management
Be cautious when it comes to multi-hypervisor management tools
Multi-hypervisor automation with Microsoft's toolkit
Most VDI implementations run one of the following major Type 1 hypervisors: VMware vSphere, Microsoft Hyper-V or Citrix XenServer. These bare-metal hypervisors run directly on the hardware, whereas Type 2 hypervisors run as an application atop the OS. Here's how to perform a virtual desktop migration between two Type 1 hypervisors.
What you need to know before you migrate
There are two ways to convert an existing virtual machine (VM) to another format. One method is to use a conversion application such as VMware vCenter Converter to do a "hot" (while the source machine is running) or "cold" (when the machine is powered off) conversion. Which tool you use depends on your VDI migration. For example, if you just need to migrate a Citrix XenDesktop VM to vSphere, you should use the VMware Converter tool.
The other way is to convert the disk formats of the existing virtual desktop directly using tools such as StarWind Software's V2V Converter or Microsoft Sysinternals Disk2vhd tool. If you need to convert a virtual desktop template that's in Virtual Machine Disk file (VMDK) format to Virtual Hard Disk (VHD) format, you could use the StarWind converter or the Disk2vhd tool.
It is possible to import and export virtual desktops using the Open Virtualization Format (OVF) packaging standard, but that process only creates a package of files that support a VM, including the disk files; it doesn't convert the disk. So before you try to convert a virtual desktop from one platform to another, you need to know which hypervisors support which disk formats:
VDI, VHD, VMDK, HDD
Then, determine which type of VDI you want to convert from and what you want to convert to. I've seen a lot of virtual desktop migrations from a Citrix XenServer hosting platform to a vSphere one, for instance. One thing to note is that VMware View does not run on any other Type 1 hypervisor except VMware's own vSphere virtualization platform.
Virtual desktop migration to vSphere
The VMware Converter tool provides the easiest and most consistent virtual desktop conversions. It allows for many options during the conversion process and provides a lot of information to help you troubleshoot issues that may come up.
VMware Converter's biggest drawback is that it's severely limited in the types of machines it will convert. Plus, you cannot schedule a virtual desktop migration via the graphical user interface (GUI).
Here are some key points to keep in mind as you prepare to convert virtual desktops with VMware Converter:
- The tool supports Hyper-V conversions but does not support XenServer or Oracle VM VirtualBox.
- You can do a hot clone in almost all cases, without being forced to power off the machine.
- Make sure to disable the services associated with the former hypervisor (such as XenTools in XenServer) in the Destination Services tab so that when the machine comes back up in its new platform, those services will not start automatically.
- Changing disks to "thin" is possible if you do vSphere-side thin provisioning.
- If you change any disk allocations, you can't do automatic synchronization of the changed deltas at the end of the conversion.
To start your VDI migration, run the tool from the machine that you want to be converted. This is the recommended best practice by VMware, even though they do give the option for a client-server setup where you can connect to and convert remote machines.
Let's use the example of migrating a XenDesktop VM to vSphere. Here are the steps involved using VMware Converter:
- Remove the machine from the Desktop Delivery Controller (DDC) catalog.
- Uninstall the Virtual Desktop (VD) Agent.
- Stop the Citrix System Monitoring Agent service, otherwise the Converter job will fail.
- Install VMware Converter.
- Set the XenTools service in the Destination Services tab to Disabled.
- Once the conversion is done, power up the machine and install VMware Tools.
- Reboot the machine.
- Install the VD Agent and recreate the machine in the DDC catalog.
Tools for Hyper-V conversion
I have had excellent luck directly converting disks to or from Hyper-V and to or from vSphere using StarWind Software's V2V Converter. This very simple GUI tool is quick and easy to use. Its process is different than using a tool like VMware Converter, which allows for hot cloning, because this tool only allows for conversion while the machine is powered off.
Other tools such as Microsoft Sysinternals Disk2vhd tool can be used when the machine is running, but the process is much slower since files are in use and there are active disk reads and writes going on during the virtual desktop migration.
VDI migration to XenServer
Citrix supplies a tool called XenConvert, but it is much more limited in functionality than its VMware counterpart. Until some recent revisions came out, many IT pros considered the product a floccinaucinihilipilification (go ahead, Google it) that only served a limited purpose.
Still, the only thing I really like in this tool is the options for the disk image output. You can convert to VHD, XVA (XenServer disk), OVF or Provisioned Services vDisk. This capability makes the conversion to XenServer much more flexible, because you may want your virtual desktop to be provisioned with Provisioning Services rather than just a standalone machine.
You can't convert disks to thin provisioning, however, and it doesn't provide the services and throttling that VMware Converter does. You also can't do any cold conversions. This offering still needs a lot of work to be useful for a VDI migration.
What about vSphere to XenServer?
As for migrating from a vSphere-hosted virtual desktop to a XenServer platform, that type of transition is difficult at best. XenServer directly supports Hyper-V's VHD format, so that type of conversion is much easier.
Plus, since VirtualBox supports them all, it's considered the easiest to migrate to. It is by far the most versatile hypervisor when it comes to conversions. It contains built-in disk image conversion tools, with which it can convert to and from many different formats, including vSphere, XenServer and Hyper-V. I just wish it were more accepted as an enterprise hosting platform for virtual desktops.
This was first published in September 2012