This Article is based on another nice article written initially in French by Laurent Falguiere.

Windows 2008 Terminal Services introduce a new functionnality called "Drain Mode".

This new functionnality allows Admins to connect to a Terminal Server while Users can not (Only disconnected sessions will be able to reconnect, while new sessions won't be allowed).

Actually, when a server is configured in this mode, only "/Admin" Sessions and Users with Disconnected Sessions are allowed to Connect to the Server.

This mode will also be detected by a Terminal Server Session Broker and then Users won't be redirected anymore to a server with this mode enabled.

This could be really useful for maintenance purposes (Applications Upgrades or before Server Reboot).

To Configure the "drain" Mode You have Two possibilities :

Using the Graphical Interface :

The "Drain Mode " is available from the "Terminal Services Configuration" Console located in the "Administrative Tools\Terminal services" Folder.

In this Tool, You have an Option Called "User Logon Mode"

Within this Option, You can Select :

• Allow All Connections (Default)
• Disable New Connections, But Allow Reconnections   
• Disable New Connections, But Allow Reconnections until Next Restart

Using the Command Line Interface :

The "change logon" command line has been adapted to manage the "Drain Settings". 

CHANGE LOGON:

• change logon  /DRAIN   
• change logon  /DRAINUNTILRESTART   
• change logon /ENABLE (To Allow Connections)