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Microsoft Exchange Server 2010 Requirements : Getting the Right Server Hardware (part 1) - The Typical User , CPU Recommendations

10/18/2014 3:52:20 AM
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One of the things that you can always depend on when looking at any manufacturer's hardware specifications is that the specs will always provide the minimum recommendations necessary to run the specified product. Microsoft has learned from their customers that recommending a minimum configuration often yields unhappy customers.

Minimum hardware configuration works just fine if you are building a test lab or a classroom environment. But for production environments you want to make sure that your hardware can support a typical everyday workload plus a bit more. In this section, we will make some recommendations that are partially based on our own experiences and partially based on Microsoft's best practices.

Note that hardware configuration can vary quite a bit depending on the server's role and its workload. You may be supporting a single server with 100 mailboxes or a multiserver site with 100,000 mailboxes. You should plan to comfortably support your maximum expected load along with some room to grow.

Choosing the Right Hardware

There are three key factors to ensuring that your Exchange servers function reliably and efficiently: stable hardware, correctly configured software, and proper management. If you fail to get any one of these right, the result will be poor performance, downtime, data loss, and unhappy users.

Windows hardware compatibility is probably the most important part of your choice for a server platform. This includes not only the server model itself, but also the components you will be using, such as network adapters and any third-party software.

Pick a server vendor that offers local support. Choose a server model that will provide you with the card slots and available disk drives. When evaluating server models, ensure that the server model is near the beginning of its model life rather than near the end. It is not uncommon to purchase a server through a discount outlet that is near or at the end of its model life.

As you build your Windows servers, ensure that you are running reasonably recent versions of all supporting software, such as device drivers, and that the operating system is patched.

1. The Typical User

If you have worked with more than one organization, you have probably reached the same conclusion that we have: no two Exchange organizations are exactly alike. Even businesses within the same industry can have dramatically different usage patterns based on slightly different business practices.

Where does this put the poor hapless person in charge of figuring out how much hardware to buy and how much capacity that hardware should have? If you are currently running an earlier version of Exchange Server, at least you have a leg up over other people.

You can use tools such as Performance Monitor to measure the number of messages sent and received per day and disk I/O capacity. You can use a tool such as the Exchange 2003 System Manager to report on mailbox sizes. You can enable message tracking and use tools such as the Exchange Server Profile Analyzer or Promodag Reports ( to report how much mail each user sends and receives per day (and more).

Microsoft has done a lot of research in this area and has published some statistics on what they consider to be light, average, heavy, very heavy, and extra heavy Outlook users. They have also calculated that the average email message size is 50 KB in size. Table 1 shows how Microsoft has defined each type of user.

Just relying on emails sent and received may not be the best judge of the hardware capacity required.

  • Email archiving

  • Mobile device user (the Blackberry can place a load four times higher on a server than a typical Outlook user)

  • Antivirus scanning

  • Messaging records management

  • Transport rules

  • Database replication

Table 1. Microsoft's Outlook User Types
User TypeMessages Sent per DayMessages Received per Day
Very heavy30120
Extra heavy40160

2. CPU Recommendations

Exchange Server 2010 only runs on Windows Server 2008 x64 and therefore only on hardware (physical or virtualized hardware) that is capable of supporting the x64 processor extensions. The processor should be at least 1.6 GHz, though you will certainly benefit from processors faster than 2 GHz and multicore processors. The processor must be one of the following:

  • Intel Xeon or Intel Pentium x64 that supports the Intel Extended Memory 64 Technology (EM64T)

  • AMD Opteron 64-bit processor that supports the AMD64 platform

The Intel Itanium IA64 processor family is not supported.

Table 2 shows the processor recommendations from Microsoft for different Exchange Server 2010 roles.

Table 2. Processor Recommendations Based on Server Role
Exchange 2010 Server RoleMinimumRecommendedRecommended Maximum
Edge Transport1 × processor core4 × processor cores12 × processor cores
Hub Transport1 × processor core4 × processor cores12 × processor cores
Client Access2 × processor core8 × processor cores12 × processor cores
Unified Messaging2 × processor core4 × processor cores12 × processor cores
Mailbox2 × processor core8 × processor cores12 × processor cores
Combined function (combinations of Hub Transport, Client Access, and Mailbox server roles)2 × processor core8 × processor cores16 × processor cores

This may seem like a lot of processor horsepower, and in some ways it sure is. But remember that an Exchange 2010 server is doing a lot more than an Exchange 2003 server. For example, on a combined-function server that is running the Mailbox, Client Access, and Hub Transport server roles, not only are the database engine, web components, and message transport running, but new components such as transport rules, messaging records management, mailbox archival, and RPC client access functions are also running.

If you have worked with Exchange Server 2007 in the past, you may also note that the CPU recommendations for the Exchange 2010 Client Access server are for more capacity than in Exchange 2007. This is because all Outlook MAPI RPC traffic has been abstracted out of the Information Store service and is now handled by the RPC client access service.

If you are planning to use existing server hardware, consult your manufacturer's documentation for specific information on the processors and cores.

If you are not sure whether your existing hardware supports the x64 extensions, you can check this in a number of ways, including confirming it with the hardware vendor. If the computer is already running Windows, you can get a handy little program called CPU-Z from that will check your processor. Figure 1 shows the CPU-Z program.

Figure 1. Using CPU-Z to identify the CPU type

Notice in the Instructions line of CPU-Z that this particular chip supports x64–86. This means that this AMD chip will support the x64 instruction sets. Intel processors will report that they support the EMT64T instruction set.

2.1. Hub Transport CPU Considerations

We don't have a specific formula that you should use when planning for the CPU requirements on a Hub Transport server. For organizations that are small enough to support all roles on a single, combined-function server, you just want to make sure that the server has sufficient CPU cores for all the tasks that all the different Exchange roles must perform.

As you start to scale your organization to the point that you are putting specific server roles on dedicated server hardware, consider the factors that utilize the CPU on a Hub Transport server. The number one factor, of course, is the number of messages transported per hour. Four processor cores will probably be sufficient for a server that transports 1,000 messages per hour, but factors that might require more CPU capacity on a Hub Transport server include the following:

  • Integrating Windows Rights Management

  • Enabling transport rules

  • Using message journaling

  • Antivirus and/or antispam scanning

  • Processing lots of large messages

  • Enabling additional transport agents

2.2. Client Access Server CPU Considerations

All access to mailbox content is now handled through the Client Access server; this was not necessarily true in previous versions of Exchange. Now, mobile devices, web clients, Outlook MAPI clients, POP3, and IMAP4 clients all go through the Client Access server.

Although this is a good thing for the Mailbox server, it means that the Client Access server has more work to do. A Client Access server in an environment with a few hundred mailboxes can probably use a two-CPU core processor, but as the number of simultaneous users climbs, the processor power required will also climb. These additional factors may affect CPU requirements:

  • Implementing SSL (secure sockets layer) access on the Client Access server

  • Supporting larger numbers of POP3, IMAP4, Outlook Web Access, or Windows Mobile clients (since these clients require messages to be converted)

2.3. Mailbox Server CPU Considerations

The number of processors required on a Mailbox server mostly depends on the total number of simultaneous users. According to Microsoft, a dedicated Mailbox server with sufficient memory and a four-processor core server should be able to support 2,000+ mailboxes. Microsoft estimates a factor for calculating CPU requirements is one CPU core for each 1,000 mailboxes; this guideline is based on some assumptions about the usage profiles of those 1,000 users. In this case, they assume that 750 of those are active and heavy usage mailboxes. Sizing your mailbox servers for 10 to 20 percent more capacity than you think you are going to need is a good practice.

A number of factors affect CPU requirements, including the usage profile of the typical user and the concurrency rate (the percentage of your users who are accessing the server at any given time). If you are planning to support 2,000 very heavy users who use Outlook 90 percent of the day, you may need more CPU capacity. Factors that affect mailbox server CPU requirements include the following:

  • Number of simultaneous users and usage profile

  • Email archiving processes

  • Mobile device usage

2.4. Scaling to Dedicated Servers Roles

For an awful lot of Exchange Server administrators, we never have to worry about more than a single server because our entire user community can fit nicely on to a single, combined function server. At some point, though, you may be required to add dedicated Exchange Server 2010 server roles to your organization. Here are some scenarios that may require dedicated server roles:

  • The Active Directory site has more than one Mailbox server role.

  • The Hub Transport, Client Access, or Unified Messaging functions place too much overhead on a single server.

  • The requirements for high availability and/or load balancing demand more than one point of failure.

Exactly how many Client Access or Hub Transport servers do you require? As with almost everything related to an Exchange Server configuration, this depends largely on your user community and the load they place on the server. Microsoft has a guideline based on the number of processor cores that the Mailbox server has versus the number of supporting Client Access or Hub Transport server processor cores.

For Hub Transport servers, this ratio will be different depending on whether or not the Hub Transport has antivirus software on it. For Hub Transport servers without antivirus software, you should plan to have one Hub Transport processor core for every seven Mailbox server cores. If the Hub Transport server has antivirus software scanning enabled, that ratio changes to one Hub Transport processor core for every five Mailbox server cores.

The ratio is different for Client Access servers partially because of the additional load placed on the Client Access server by the RPC client access component. A typical environment should have three Client Access CPU cores for every four Mailbox server cores.

If you have a dedicated Mailbox with eight CPU cores, a dedicated Hub Transport server (with antivirus scanning enabled) should have two CPU cores. The Client Access server should have six CPU cores. This configuration provides no redundancy and does not take into consideration any additional factors that might increase processing load, such as enabling SSL, or many transport rules.

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