Exchange Server 2010 server roles (part 1) - Mailbox Server role

1/13/2011 4:11:48 PM
Up until Exchange Server 2003, all roles were installed on one server and administrators were unable to select which features were available. It was possible to designate an Exchange 2000 or Exchange 2003 server as a so called "front-end server", but this server was just like an ordinary Exchange server acting as a protocol proxy. It still had a Mailbox Database and a Public Folder database installed by default.

Exchange Server 2007 introduced the concept of "server roles" and this concept is maintained in Exchange Server 2010. The following server roles, each with a specific function, are available in Exchange Server 2010:

  • Mailbox Server (MB) role

  • Client Access Server (CAS) role

  • Hub Transport Server (HT) role

  • Edge Transport Server (Edge) role

  • Unified Messaging Server (UM) role.

These server roles can be installed on dedicated hardware, where each machine has its own role, but they can also be combined. A typical server installation, for example in the setup program, combines the Mailbox, Client Access and Hub Transport Server role. The Management Tools are always installed during installation, irrespective of which server role is installed.

By contrast, the Edge Transport Server role cannot be combined with any other role. In fact, the Edge Transport Server role cannot even be part of the (internal) domain, since it is designed to be installed in the network's Demilitarized Zone (DMZ).

There are multiple reasons for separating Exchange Server into multiple server roles:

  • Enhanced scalability – since one server can be dedicated for one server role, the scalability profits are huge. This specific server can be configured and optimized for one particular Role, resulting in a high performance server.

  • Improved security – one dedicated server can be hardened for security using the Security Configuration Wizard (SCW). Since only one Server Role is used on a particular server, all other functions and ports are disabled, resulting in a more secure system.

  • Simplified deployment and administration – a dedicated server is easier to configure, easier to secure and easier to administer.

I will explain each server role in detail, in the following sections.

1.6.1 Mailbox Server role

The Mailbox Server role is the heart of your Exchange Server 2010 environment. This is where the Mailbox Database and Public Folder Database are installed. The sole purpose of the Mailbox Server role is to host Mailboxes and Public Folders; nothing more. In previous versions of Exchange Server, including Exchange Server 2007, Outlook clients using MAPI still connected directly to the Mailbox Server Role, but with Exchange Server 2010 this is no longer the case. MAPI clients now connect to a service called "RPC Client Access," running on the Client Access Server. (The original code name of RPC Client Access was "MAPI on the Middle Tier" or MoMT.)

The Mailbox Server Role does not route any messages, it only stores messages in mailboxes. For routing messages, the Hub Transport Server role is needed. This latter role is responsible for routing all messages, even between mailboxes that are on the same server, and even between mailboxes that are in the same mailbox database.

For accessing mailboxes, a Client Access Server is also always needed; it is just not possible to access any mailbox without a Client Access Server.

Figure 1. The Mailbox Server role is hosting Mailboxes and Public Folders.

As I mentioned, Storage Groups no longer exist in Exchange Server 2010, but mailboxes are still stored in databases, just like in Exchange Server 2007. Although rumors have been circulating for more than ten years that the database engine used in Exchange Server will be replaced by a SQL Server engine, it has not happened yet. Just as in earlier versions of Exchange Server, the Extensible Storage Engine (ESE) is still being used, although major changes have been made to the database and the database schema.

By default, the first database on a server will be installed in the directory:

Figure 2. The default location for the Mailbox Databases and the log files.

The <<identifier>> is a unique number to make sure that the Mailbox Database name is unique within the Exchange organization.

It is best practice, from both a performance and a recovery perspective, to place the database and the accompanying log files on a dedicated disk. This disk can be on a Fiber Channel SAN, on an iSCSI SAN, or on a Direct Attached Storage (DAS) solution. Whilst it was a design goal to limit the amount of disk I/O to a level where both the database and the log files could be installed on a 1TB SATA disk, this is only an option if Database Copies are configured and you have at least two copies of the Mailbox Database, in order to avoid a single point of failure.

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