Exchange 2007 introduces a new Exchange term: "Server Role". Server role is a logical concept used to organize Exchange 2007 services and features across one or more servers. While Exchange 2003 provided primitive server roles called BackEnd server and FrontEnd server, Exchange 2007 has more granular divisions.
Dividing Exchange features among several server roles has advantages:
- More flexible deployment topology: For a small or medium company that has only hundreds of mailboxes and all users are centralized, customer can install all required roles on one physical server. For a large enterprise where tens of thousands of mailboxes span multiple physical locations, customer can choose to deploy each role on a separate server or even multiple servers per role to provide better performance and fault tolerance.
- Better hardware utilization and scalability: Because each role only installs binaries and runs services for a specific feature set. Unlike older versions of Exchange, configuring a server that has only one or two roles will reduce Memory, CPU and disk space requirements for this server. In addition, roles are scalable so admin can load balance work of one role to multiple servers.
- Easy to maintain: Upgrading, applying hotfix, or other server changes that could cause server outage can be isolated to one server role. This reduces maintenance down time and end user impact. Admin can also install or uninstall roles on a server as needed.
So what are these roles anyway? During the beta releases of Exchange 2007, there were 6 planned roles. They were: Mailbox, Public Folder, Client Access, Edge, Bridgehead and Unified Messaging. As Exchange 2007 development progressed, Public Folder role was merged into Mailbox role since they share Extensible Store Engine and MAPI access. Additionally, "Bridgehead" role was renamed to "Hub Transport" to more clearly illustrate its functionality.
At Exchange 2007 release, the server roles will be:
- Mailbox (MB): The Mailbox server role is responsible for hosting mailbox and public folder data. This role also provides MAPI access for Outlook clients. Note that there is also a variation of this role called Clustered Mailbox role, for use with high-availability MSCS clustering of mailbox data. When Clustered Mailbox role is selected, other server roles cannot be combined on the same physical server.
- Client Access (CA): The Client Access server role provides the other mailbox server protocol access apart from MAPI. Similar to Exchange 2003 FrontEnd server, it enables user to use an Internet browser (OWA), 3rd party mail client (POP3/IMAP4) and mobile device (ActiveSync) to access their mailbox.
- Unified Message (UM): This role enables end users to access their mailbox, address book, and calendar using telephone and voice. IP-PBX or VoIP gateway needs to be installed and configured to facilitate much of the functionality of this server role.
- Hub Transport (HT): The Hub Transport role handles mails by routing them to next hop: another Hub Transport server, Edge server or mailbox server. Unlike Exchange 2003 Bridgehead that needs Exchange admin defined routing groups, Exchange 2007 Hub Transport role uses AD site info to determine the mail flow.
- Edge Transport (ET): The last hop of outgoing mail and first hop of incoming mail, acting as a "smart host" and usually deployed in a perimeter network, Edge Transport provides mail quarantine and SMTP service to enhance security. One advantage of this role is that is does not require Active Directory access, so it can function with limited access to the corporate network for increased security.
Server Roles Deployment
Mailbox, Client Access, Unified Message and Hub Transport can be installed in any combination on one physical server. This combined topology is well-suited for small and medium size customers. Alternately, administrators can segment these roles across multiple servers, potentially located in different domains and sites to support a large number of users or meet geographical deployment requirements. Note that if Mailbox role is installed on different physical server from Hub Transport and Client Access role, the Mailbox server will need to have at least one Hub Transport and Client Access server available in the Mailbox server's AD site.
Edge Transport server role, however, must be installed as the only role on a physical server. It cannot be installed in combination with any other server role.
Even after the server has been installed, Admin can install new roles or uninstall existing roles. Note that Client Access and Unified Messaging server roles of Beta Exchange 2007 do not support build-to-build upgrade. This means if you have Beta 1 Client Access or Unified Message server roles installed and want to upgrade to Beta 2, you need to uninstall these roles first then install them with Beta 2.
All server roles can co-exist with Exchange 2003 servers. To migrate, you should install server roles in this order: Client Access, Hub Transport, Mailbox and Unified Messaging. Edge transport can be installed separately from the migration planning, either before, during, or after the other Exchange 2007 server roles. After replacing Exchange 2003 front-end with Exchange 2007 Client Access server, an Exchange 2003 mailbox user still can use OWA to access their mailbox through the Exchange 2007 CAS server's /Exchange virtual directory (for example: http://<server FQDN>/Exchange).
Please note these two known issues:
1. In Beta 2, if the Client Access server also has Mailbox server role installed, OWA won't work for Exchange 2003 mailbox user. The workaround is to install Client Access server role and Mailbox server role on separate servers.
2. The first Mailbox server role installed into an Exchange 2003 organization should not be installed with cluster continuous replication (CCR). This is because the first Exchange 2007 Mailbox server role added in Exchange 2003 organization will try to create a public folder database and public folder replicas which can't take advantage of CCR. We will write about this separately.
Server Role Tasks and UI
Server configuration for both Cmdlet and GUI is organized around the server role concept. To check what roles are installed on the server, you can use task: Get-ExchangeServer and check properties: IsMailboxServer, IsClientAccessServer, IsHubTransportServer and IsUnifiedMessagingServer. For each role, Exchange 2007 provides dedicate tasks to manage properties specific to each server role:
Note that Get/Set-TransportServer is used by both Transport server roles (Hub Transport and Edge Transport). Please refer to help for more detailed info regarding these tasks.
In Exchange 2007 management console under Server Configuration, each server role has a dedicated node with the role name. Servers with the selected role installed will be listed in the results pane for each server role node. A single server will appear in multiple results panes if multiple server roles are installed on that server. This design gives user a clear view on what servers are available for each specific server role.