Does a TFS 2010 backup require the server to be offline?

I have been told that our TFS 2010 server must be taken offline during the backup process, which means that th开发者_如何学Cere is a chunk of time every night where the server is unavailable.

I have searched through the TFS documentation, and writeup of using TFS Power Tools for backup (http://msdn.microsoft.com/en-us/library/bb552295.aspx and http://blogs.msdn.com/b/bharry/archive/2010/08/18/backing-up-and-restoring-your-tfs-server.aspx), and have been unable to find anything that indicates either way.

Is it possible to keep the TFS 2010 server online during a backup, or must it be taken offline?