The Terminal Services Session Directory service is a database that keeps track of sessions on terminal servers in a cluster and provides the information used at connection time to connect users to existing sessions. In this article I discuss this and also how to create a Terminal Server Cluster.

 
 To setup a Terminal server cluster using the session directory you will need the following:
 
 Two or more Windows 2003 servers (Must be at least Enterprise or Datacentre edition).
 The network cards in these servers must be load balanced (Typically using Network Load Balancing or DNS Round Robin)
 A server for the session directory. Microsoft recommend that this is a separate highly available server not running Terminal Server.
 
 As stated above it is recommended that the session directory is held on a separate server. This can actually be installed on one of the servers in the cluster but as well as performance issues you would be unable to take this server offline without impacting the whole cluster.
 
 To start the session directory simply go to admin tools, services and start the “Terminal Services Session Directory” service. To ensure this starts automatically every time the server starts click the start-up type and set to automatic.
 When the service is started it will create a “Session Directory Computers” local group. By default this will be empty and you can add in the Terminal Servers to this group.
 
 If you place all the Terminal Servers in an OU within Active Directory you can then apply a group policy to them to create a cluster. Within the group policy locate Windows Components/Terminal Services/Session Directory, click enable and specify the name of the server running the “Terminal Services Session Directory” service.
 
 Remember when you have set this up to point the RDP clients to the cluster ip address and not individual server ips.
 
 
 How the Process works
 
 When a user logs on to the terminal server cluster the session directory server gets to know about it as the Terminal Server who receives the login request sends this information to it. The session directory service then checks the username to see if the user has any disconnected sessions. If the user doesn’t have any then the request is sent back to the Terminal Server and logon continues. If the user does have a disconnected session on another servcer then the logon request is sent to tht server instead and the user logs on to the disconnected session. The session directory is then updated.
 
 Other Documentation on this site
 How to Configure Network Load Balancing
 Configuring the Citrix Load Evaluators