This article explains slow logon times for XenDesktop v7.1. In addition to slow logons, the wallpaper may show as black during the initial logon process.
A slow logon is a relative thing and depends on a myriad of factors. If your server or desktop logon does not show the progress wording on logon but instead has only black wallpaper then it is definitely worth testing out this registry key. If you just think that your logon is slow, then it still may be worth the effort to test.
Add a new registry key to the master image (desktop or server).
Before you add the key, establish a logon time baseline. I historically like to do this manually using a stopwatch (iPhone) but the built in Director logon time functionality is an exciting new feature and will give you additional insight. Here is an example of a Windows 7 baseline from the SageLike lab:
After adding the key, time another logon to see if your logon duration has improved. Here is an example of the after:
This is a big improvement but YMMV. An interesting side effect for Windows 2008 R2 server deployments is the return of the status text while establishing a session. A blank black screen leaves the user to wonder if anything is happening at all. This fix replaces the black wallpaper with the rapidly changing logon status information. This cues the user that many things are happening to build their session.
I have not found the history of this registry key or why it is absent when using the v7.1 VDA. I have observed this working quite well for both Windows 7 and Windows 2008 R2 in a lab environment. At the time this was written, the reference CTX article below only indicates it is applicable to XenApp 6.5
SageLike Post ID: SL0006
Windows 2008 R2
CTX135782 Black Screen Logging on to a Published Desktop