Recently, a customer was experiencing a XenApp 7.x server that frequently “unregistered” with the XenDesktop 7 DDCs. The problem was resolved by resetting the performance monitoring counters with the command lodctr -r.
I’ve seen this type of thing happening on Citrix servers for years, but basically when an incoming ICA connection is made, Citrix will determine where to place the user based on a “load” value between 0-10,000. A load of 10,000 means the server if full and it will not accept additional ICA connections. However, in my experience, 10,000 has been an erroneous load value the majority of the time.
To determine the load of the server, Citrix uses Windows performance counters. I found the following on the Citrix support site:
The load balance concept of XenApp depends on the use of Windows Performance Monitor counters to run the test and receive the correct statistics. If this is damaged or not installed correctly, XenApp will not be able to get a correct read, thus forcing a load of 10000 because the tests are failing.
Based on what I have seen this week, it looks like this problem can occur on servers running the XenDesktop 7.x VDA.