In my last post I blogged about recovering from a crashed AT. TFS also supports a warm standby of AT. This helps you fail over to the warm standby AT when the primary AT fails. This is really great as it reduces the recovery time. You can setup a warm standby by running TFS 2008 setup and provide existing DT machine as input. TFS setup will detect the primary AT is different machine and automatically install a warm standby for you.
If you have warm standby and your primary AT machine crashes you can activate the standby AT and make it the primary AT by running TFSAdminUtil command line tool with ActivateAt option.