Public folder replication is the process by which public folder content and hierarchy are replicated across multiple servers for fault tolerance. Public folder databases replicate two types of public folder information, hierarchy and content. Each public folder database retains a copy of the hierarchy where as content replicas exist only on the public folder databases that you configure. If you find that the public folder hierarchy on one server is different from the public folder hierarchy on other servers, you can synchronize the hierarchy using Update-PublicFolderHierarchy cmdlet.
Unlike in Exchange 2007 (CCR with only one public folder database in the org), you can’t use continuous replication in Exchange 2010 to replicate public folders. In Exchange 2010, continuous replication is only for mailbox databases. A public folder database can be hosted on a mailbox server which is a member of a DAG, but you must configure multiple public folder databases across servers and configure public folder replication for data redundancy.