This article contains information about separating the roles of Farm Master and Controller in the XenDesktop Farm.

Background

By default, in a XenDesktop farm, the initial Desktop Delivery Controller (DDC) installed is the farm master with specific duties as the Data Collector, performing desktop resolution operations during starting the desktop and managing the hosting infrastructure. This single server has the role of Data Collector and Controller. When there are multiple servers in a farm, it is often required to separate the functions of Controller and Data Collector through delegating these functions to different servers. Other Desktop Delivery Controller machines in the farm can perform these other duties so that the farm master machine can concentrate on its own role requirements.

To separate the roles, complete the following actions:

• Ensure to choose a particular machine to be the farm master.

• Ensure that the farm master machine does not perform unnecessary duties.

Controlling Farm Master Election

Each Desktop Delivery Controller machine in the farm can potentially become the farm master in an election process. This settings on various server machines can influence election process, and one or more machines can be indicated as preferred as being farm master, and other machines only take on the farm master role if the preferred machines are unavailable. This preference indication is achieved with the use of registry entries on various server machines. Each machine can be configured to have one of the four possible settings:

• Master: servers with this setting are preferentially chosen as the farm master. Often, only one server in the farm would have this setting.

• Backup: servers with this setting are preferentially chosen as the farm master when the master server is unavailable.

• Member: servers with this setting are normally not the farm master, but can assume the farm master role when none of the master or backup servers is available.

• Slave Only: servers with this setting are not eligible to be the farm master.

To configure a server machine to one of these settings, complete the following procedure:

Caution! Refer to the Disclaimer at the end of this article before using Registry Editor.

If using a 64-bit Operating System, the following registry keys apply to the WoW6432Node section of the registry:

1. Set the HKLM\Software\Citrix\IMA\RUNTIME\UseRegistrySetting DWORD registry entry to 1.

2. Set the desired master ranking value in the HKLM\Software\Citrix\IMA\RUNTIME\MasterRanking DWORD registry entry to one of the following values:

   • 1 indicates ‘Master’
   • 2 indicates ‘Backup’
   • 3 indicates ‘Member’
   • 4 indicates ‘Slave Only’
3. Restart the server.

Note: UseRegistrySetting reverts to 0 after the IMA service starts. The IMA service updates the data store when the value is set to 1, then changes the value back to 0 so it is not updated on subsequent starts. In addition, MasterRanking is set to the value present in the data store upon IMA start if UseRegistrySetting is set to 0. This allows the administrator to view the current ranking on each DDC.

Controlling Brokering Duties on the Farm Master

The main set of duties that can be avoided on the farm master DDC server are those associated with managing the status and operations of individual Virtual Desktop Agent (VDA) machines. You can achieve this through setting a registry entry on the farm master server to limit the number of VDA worker machines that the farm master agrees to administer. Again, this involves changing the registry, so a backup of the registry is advised prior to making any changes.

To limit the number of VDA worker machines allowed to register with a DDC server machine, and to be directly administered by that DDC server, set a value in the following DWORD registry entry on the DDC:
HKLM\Software\Citrix\DesktopServer\MaxWorkers

The value represents the number of VDA machines that can register with this DDC.

The smaller the value in the registry entry, the fewer worker machines the server can accept, the value zero indicates that the server cannot accept registrations from any VDA worker machine, which forces all the VDA worker machines to register with other DDC server machines in the farm.

Note: Distributed farm deployments of XenDesktop are not supported. There is only one IMA Data Collector per farm. It is recommended to create multiple farms for geographically dispersed deployments.

Caution! Using Registry Editor incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

Setting DDC roles in a XenDesktop Farm