Microsoft IT recently published a paper detailing their early-adopter experience with TS in Windows Server 2008. They share some server sizing best practice recommendations, viz:

Best Practices

By deploying Terminal Services 2008 in both small and large environments worldwide, the deployment team developed the following best practices that it considers important to the successful deployment of a Terminal Services environment:

  • Limit computer-based NLB implementations to TS Gateway deployments that experience 1,500 or fewer simultaneous connections. The team calculated that Windows NLB would work best with a maximum of approximately 1,500 simultaneous connections. Adding more load-balancing servers would not appreciably increase the number of connections that the TS Gateway farm can host. For TS Gateway farms that experience more than 1,500 simultaneous connections, using a third-party load-balancing device is the best approach.
  • Deploy three or more NLB nodes to support TS Gateway in an NLB cluster. The maximum number of connections that a single NLB cluster node can support is limited by the CPU resources of that node. Depending on the CPU speed and other hardware resources of each cluster node, the team determined that three or more cluster nodes may be required in an NLB environment with a maximum of 1,500 connections for the whole NLB cluster.
  • Install TS Session Broker on a separate computer. The team found that to have the most flexibility in a load-balanced terminal server farm, the TS Session Broker component should run on a separate server. This type of installation enabled the team to take any terminal server offline for maintenance or upgrade purposes without affecting the availability of the terminal server farm. The team found that the hardware resources that the TS Session Broker computer requires are very light. Therefore, the team determined that the TS Session Broker role could be installed on a less capable computer, or the role could be combined with other roles in the organization.