In a recent article Brian Madden described the new Login Throttling load evaluator options introduced in Citrix Presentation Server 4.5. The purpose of the Login Throttling options is to control the behavior of the Load Bias and to prevent the Black Hole effect. Ericom Software PowerTerm WebConnect Load Balancer has had a built-in mechanism to prevent the Black Hole effect from its very first version. Since this mechanism is different than the one introduced in CPS 4.5 I think its worth while to describe its operation.
Using the PowerTerm WebConnect admin console you can specify how many logons a Terminal Server can handle in a given period of time. By default a total of 10 client sessions can connect to the same Terminal Server within a period of 20 seconds. Once this number of sessions has connected no additional sessions will be directed to this server for the remainder of the duration, regardless of the load on this server or any other server in the farm. We call this feature “Onrush Blocking” – See image on the left.
So why did we choose this mechanism? Because: