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Five things to know before a XenDesktop farm migration

Migrating a lot of VMs from one XenDesktop farm to another is a daunting process, but with some research and planning, it doesn't have to be so hard.

LAS VEGAS -- When it comes time to migrate a Citrix XenDesktop farm -- whether it's for disaster recovery, setting up parallel sites or to do a hardware upgrade -- there are some things IT can do to make its job easier.

It's important for administrators to understand how the entire migration works and to set realistic expectations. In a session here at Citrix Synergy 2016, Shane O'Neill, senior engineer at Aetna, and Paul Stansel, principal consultant with Presidio, shared these five things to keep in mind during the XenDesktop farm migration process:

Hardware upgrades are unavoidable and necessary.

It helps to go into a migration having accepted that it's a somewhat painful process. Remember that others have migrated farms before you and will migrate after you. Hardware upgrades and migrations are just part of the IT circle of life.

You will run into problems.

Whether it's challenges with Microsoft's Virtual Desktop Access (VDA), Universal Unique Identifier (UUID) or other aspects of a migration, expect to spend some time troubleshooting and fixing problems. One of the most common issues that comes up is when UUIDs don't match, O'Neill and Stansel said. The UUID is the name the controller uses to call XenDesktop VMs from the server, and the IDs need to be the same on both ends. If you're trying to migrate and you get an error that says power state unknown, you probably have mismatched UUIDs.

To fix this issue, one option is to correct the UUIDs by hand so they match, but that's not realistic in large-scale deployments. The other option is to follow some of the troubleshooting options from Citrix support, which Stansel and O'Neill said should help solve any UUID problems.

Another common problem with migrating XenDesktop farms is a lack of tools to simplify the process. Admins may choose to migrate manually -- again, not an ideal option in large deployments -- or script the process using PowerShell commands. Third-party tools, such as Stansel and O'Neill's XenDesktop Farm Migration Utility, are another option.

"VDA is God."

VDA, which controls how virtual desktops are authorized, can cause a lot of problems for migrations, and there's no way around using it.

"If you"re on a persistent machine, VDA is God," Stansel said.

When setting up a new farm, the admin tells the machine catalog which version of the VDA is in use, but in the background there's a PowerShell script that determines the VMs' functional level. The VDA is backward compatible, but not forward. Therefore, if moving to a new VDA, IT must remove the old VDA and install the new one beforehand. Removing the old VDA requires manual cleanup because there's no option to perform a clean uninstall.

Stansel and O'Neill advised attendees to always install the VDA after installing or upgrading VMware Tools, because Citrix and VMware both install graphics drivers, and they try to override one another. Citrix's drivers need to be installed last. And every VMware Tool's upgrade requires reinstalling the VDA.

Policy migration doesn't work how you think it does.

Policies from one XenDesktop farm don't automatically sync to the other in Citrix Studio. The PowerShell SDK only allows for the import and export of policies within the same site. It might look like the process works between farms, but there will likely be some policies that don't transfer, which can cause more problems down the line. It's better to move the policies manually or, in a big deployment, by using Group Policy Objects.

Don't forget the components.

XenDesktop site components, such as Director, Storefront and Provisioning Services, don't need to be the same version as the XenDesktop software itself. It's important to keep an eye on the features and functionality in new versions, however, and it's a good idea to upgrade components. For customers on the Long Term Service Release (LTSR), the components do need to match the LTSR version, which is a requirement for Citrix support.

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