Plan Redundancy

Plan virtual units so that they have instances at least on two different physical servers. During a possible server failure the High Availability Control (HAC) moves services automatically on other servers. Distributing the primary instances on different servers will also even the load in normal conditions.

Take load balancing into account also when arranging the backup instances.

Planning Redundancy of Virtual Units

1. Virtual unit can have one active instance, and one or more instances as spare. Some software packages can only have one instance running at a time. Place such software in one virtual unit and instantiate it on two or more servers, so that one of the instances is the primary and the others are used as spare. For example, Terminal Server in SP08 had to be installed in this way.

   Note:

   As of 1608, there is no separate installation package for Terminal Server: the functionality has been moved to Agent Server.

2. Several virtual units sharing load: Most software package can be installed in two or more virtual units for load balancing in addition to redundancy. For example, Call Dispatcher, Bridges, Connection Server, and Data Collector are such packages. As of SP08, also all chat packages can be installed in this way.