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Virtualization of the Unified Messaging Role in Exchange 2010 SP1

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Applies to: Exchange Server 2010 SP3

Many organizations today rely on some degree of virtualization to run Microsoft Exchange Server 2010. Virtualization of the Unified Messaging (UM) role on the 64-bit edition of Windows Server 2008 R2 is supported starting in Microsoft Exchange Server 2010 Pack 1 (SP1).

Required hardware and software

The virtualized UM server must be running as the guest operating system under Windows Server 2008 R2 Hyper-V. Windows Server 2008 R2 Hyper-V is a powerful virtualization technology that lets organizations take advantage of the benefits of virtualization without having to buy third-party software. By deploying Exchange 2010 together with Windows Server 2008 R2 Hyper-V technology, an organization of any size can avoid the complications that can arise from dealing with third-party virtualization software vendors.

An Exchange 2010 SP1 server that is running the UM server role must be the only Exchange role within a single virtualized server or Hyper-V environment. Other Exchange 2010 server roles, such as Client Access, Edge Transport, Hub Transport, and Mailbox, are not supported in the same virtualized server as the UM server role.

We recommend that the computer that is running the virtualized UM server have at least four CPU cores, and at least 16 GB of memory. For virtualizing UM, the essential requirement is a 1-to-1 mapping of physical cores to virtual cores, and no overbooking. We recommend that the virtualized UM be configured to use at least 2 GB of RAM per core.

In this configuration, a virtualized UM server that experiences a typical mixture of user and caller interactions can handle fewer concurrent calls than a physical UM server that has the same specifications. Under a sustained load, tests show that a virtualized UM server that is configured as described can handle 40 concurrent calls if Voice Mail Preview is active for all UM users, and it can handle 65 concurrent calls if Voice Mail Preview is not in use.

UM does some media (audio) I/O and processing. For the production and consumption of this media, the UM role must be able to keep up with the demands of other endpoints or the user experience will suffer. For example, users may notice audio dropout, either directly for playback or indirectly if speech recognition accuracy is affected.

Facts to consider before deploying UM in a virtualized environment

When you deploy UM servers in both a physical and a virtualized environment, you must consider multiple factors that can affect your Exchange environment:

  • The number of mailboxes that are enabled for UM

  • The number of incoming calls that are processed

  • Whether Voice Mail Preview is enabled for UM-enabled users

  • The amount of RAM and the number of processor cores per UM server

In typical UM deployments, the ratio of UM-enabled mailboxes that are served to concurrent calls is at least 100:1. This is because the amount of time that a UM server spends in servicing requests (such as recording messages or using Outlook Voice Access) for any given user usually amounts to a few minutes per day. Therefore, a UM server role, virtualized as described, supports about 4,000 UM-enabled mailboxes if they all have Voice Mail Preview enabled, and about 6,500 mailboxes if Voice Mail Preview is not enabled.

A virtualized UM server role can handle fewer concurrent incoming calls than a physical UM server with the same specifications. Concurrent incoming calls include incoming calls such as call answering or voice mail calls, fax calls, Outlook Voice Access calls, and calls that are answered by UM auto attendants.

A virtualized UM server that is running under Hyper-V can process approximately 40 concurrent incoming calls when Voice Mail Preview is active for all UM-enabled users, and can handle 65 concurrent calls if Voice Mail Preview is not active.

Voice Mail Preview is a UM feature that provides users a text version of their voice messages. The text is generated by automatic speech recognition, and is included with the voice message when it is delivered. Voice Mail Preview is supported in 7 UM language packs (US English, Canadian English, French, Italian, Spanish, Portuguese, and Polish).

If Voice Mail Preview is used, a UM server throttles Voice Mail Previews if the UM server is too busy or is overloaded with incoming calls. Therefore, the percentage of voice messages that include a transcription may be less than 100 percent, depending on the UM configuration and the environment. To be reasonably sure that all average-length voice messages contain voice mail preview text, we recommend that you set the number of concurrent incoming calls to be processed by a virtualized UM server to about 25 instead of 40.

Administrators who must run UM in an environment in which voice mail usage is much heavier than usual should reduce these values. If users receive an average of 10 or more voice messages per day, or use Outlook Voice Access for more than five minutes per day, the ratio of UM-enabled mailboxes that are served to concurrent calls will be nearer to 30:1.

Generally, a UM server role, virtualized as described, should support about 4,000 UM-enabled mailboxes if the mailboxes all have Voice Mail Preview enabled, and about 6,500 mailboxes if Voice Mail Preview is not enabled.

More Information

The Exchange 2010 UM role provides voice mail services, and consolidates voice mail and email messages into a user’s Inbox. For more information about the UM server role, see Voicemail with Unified Messaging in Exchange 2010.

An organization might have many different reasons to want to virtualize an Exchange environment. The most common reasons for most organizations are as follows:

  • To consolidate underused Exchange servers onto one physical server for increased hardware utilization.

  • To consolidate Exchange Client Access server (CAS) and HUB server roles into a virtualized environment together with other server roles on the same or different physical servers (especially useful for small and medium-sized organizations or for branch offices of large organizations).

  • To save space, power, and cooling for the servers that are running Exchange.

Exchange can be virtualized on one or more servers. A small organization can have a single server that provides all the required Exchange roles and functionality. A large organization requires a more complex configuration in which the Exchange roles are installed on multiple servers for the CAS, Hub Transport, Edge, Mailbox, and UM roles. Each of these roles includes its own unique workload characteristics. Typically, the different server roles work most intensively with the following components:

  • Mailbox: processor, memory, disk

  • CAS: processor, memory

  • Hub Transport: memory, disk

  • UM: processor, disk

You must perform careful planning and workload balancing for all of the server roles to determine the optimum configurations. All server roles can be expanded to additional servers to provide high availability and failover for your Exchange environment.

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