What is TS server drain mode?

How to put a terminal server into drain mode?

There are two ways an administrator can put a terminal server into drain mode: 1) using the command-line tool chglogon.exe, or 2) using Terminal Services Configuration UI.
1. Command-line settings

The command-line tool chglogon.exe (or “change logon”) may be used to configure the drain mode. There are five options: /QUERY, /ENABLE, /DISABLE, /DRAIN, /DRAINUNTILRESTART, as shown in the following screen shot:



By default, all connections are allowed on a terminal server. To configure a server into drain mode, use the /DRAIN option.



To configure a server into drain mode temporarily, use the /DRAINUNTILRESTART option. After restart, user logons will automatically be re-enabled:



To take the server out of drain mode and restore connectivity, use the /ENABLE option:



The “chglogon /DISABLE” command has the same behavior as in Windows Server 2003 – no remote connections will be allowed, even if a user has an existing session.
2. Terminal Services Configuration UI

Terminal Services Configuration UI (Administrative Tools -> Terminal Services -> Terminal Services Configuration) is the other way to configure TS server drain settings:



The UI shows the current status of the drain mode. Double-clicking “Terminal Server Drain Mode” brings up another dialog box:



The three settings listed are defined as follows:
“Allow new user logons” – All remote connections are allowed
“Deny new user logons” – Terminal Server is in drain mode
“Deny new user logons until restart” – Terminal Server is in drain mode until the server is restarted

Update: The settings are changing slightly:
“Allow all connections” – All remote connections are allowed
“Allow reconnections, but prevent new logons” – Terminal Server is in drain mode
“Allow reconnections, but prevent new logons until the server is restarted” – Terminal Server is in drain mode until the server is restarted

Also, the above blog post is accurate for Longhorn Server Beta3. There is a minor change for RC1 in the TsConfig UI – now the drain mode is called "user logon mode"