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Weighing Exchange 2010 hardware requirements vs. organizational needs

Aligning with Microsoft’s Exchange 2010 hardware requirements is critical, but remember, you've got to balance them with your company’s own unique needs and budget.

As with other software products, Microsoft specifies the hardware requirements for Exchange Server 2010. But every organization’s needs are different and the general requirements provided may be inadequate or overkill.

Microsoft provides guidance on various hardware requirements, from the amount of disk space required to the minimum screen resolution, but certain aspects should take precedence over others. Organizations preparing to deploy Exchange 2010 should consider memory, processing power and I/O storage in order to make the most of their hardware budgets.

Exchange 2010 memory requirements
The amount of memory that Exchange 2010 requires depends on which server roles you choose to install. Microsoft recommends 4 GB for any of the Exchange 2010 server roles. However, the amount of memory you actually need depends on how heavily you use your server.

For example, the minimum supported memory for running the hub transport, client access and mailbox server roles is 8 GB. But small Exchange deployments with fewer than 10 users (or lab deployments) often get by with as little as 4 GB of memory. Microsoft does not support this setup.

For optimal performance, Microsoft recommends basing memory on the number of cores in the server. For the edge transport and hub transport server roles, Microsoft recommends 1 GB per core, with a 4 GB minimum. For the client access and unified messaging server roles, Microsoft recommends 2 GB per core, with an 8 GB minimum for the client access role and a 4 GB minimum for the unified messaging role. In my experience, 4 GB of memory is usually inadequate for a production unified messaging server.

Microsoft recommends that mailbox servers be equipped with a minimum of 4 GB of memory plus 3 MB to 30 MB of extra memory for each mailbox. That’s a big range. The amount of memory you need depends on how heavily company workers use Exchange.

If each user sends and receives only a few messages each day, then 3 MB per user may be realistic. However, users who send and receive high volumes of mail or who work with large attachments require more memory. The same can be said for users who rely heavily on features like calendaring and unified messaging.

When deciding how much memory to equip your server with, remember to account for future growth. Base your calculations on the number of mailboxes you expect to host in three years, calculate the memory requirements, then add 10% to account for unanticipated growth. Another option is to purchase a server whose memory can be upgraded when the need arises.

Exchange 2010 processing requirements
Exchange 2010’s CPU requirements are more straightforward than its memory requirements. As a rule, each server role requires a minimum of two CPU cores, save for the edge transport and hub transport server roles, which can run on a single core.

The minimum number of CPU cores for servers hosting multiple Exchange Server roles is also two. Keep in mind that these are minimum requirements. I recommend never using fewer than four cores.

Although these are Microsoft’s primary guidelines for Exchange, there are three other aspects you should take into account when shopping for a server.

  1. While it’s possible to improve Exchange 2010’s performance by adding CPU cores, the server’s performance will suffer if you have too many CPU cores. You should use a maximum of two physical CPUs and 12 CPU cores (total). The exception to this rule is that servers hosting the client access, hub transport and mailbox server roles can use up to four physical CPUs and up to 24 cores (total).
  2. Clock speed is another important consideration. If two CPUs have the same number of cores, the one with the higher clock speed will almost always be faster. Higher clock speeds mean better performance.
  3. Microsoft recommends that administrators disable Hyper-Threading. This Intel technology allows a single processor core to be treated as two separate cores, and Hyper-Threading provides an easy boost to the number of logical cores within a system. In the case of Exchange Server, however, Hyper-Threading adds CPU overhead and actually hurts the server’s performance, which is why Microsoft recommends disabling it.

Exchange 2010 storage I/O requirements
Microsoft places a lot of emphasis on the amount of disk space required by Exchange 2010, but disk I/O is just as important. I recommend using one physical disk for the Windows Server OS and another for Exchange Server binaries. With this installation, Exchange consumes roughly 1.4 GB of space, plus another 500 MB for each unified messaging language pack.

You should also dedicate a disk to the Windows page file. This should be a physical disk, not a volume on the disk containing the system volume. Placing the page file on a dedicated disk offloads paging-related I/O from the system disk, resulting in better performance.

In addition, you’ll need a separate location to store Exchange Server 2010 data. Microsoft’s recommendations vary depending on server roles and how heavily the server is used. When it comes to hub transport and edge transport servers, you need a disk to store the message queues.

If your organization doesn’t have a lot of users, you can probably get away with a standard 10,000-rpm hard drive. Low-end environments can use cheap, almost consumer-grade hardware. In environments with large volumes of mail, however, it’s better to place the message queues on a stripe set because it increases available I/O to meet demand.

A mailbox server will ideally have two RAID 1+0 arrays (stripping + mirroring) attached to it. One array stores the transaction logs, while the other stores the mailbox database.

If this configuration is beyond your budget, you can opt for a lower-end solution. In any case, the transaction logs and the mailbox database should be stored on separate physical disks. That way, if the volume containing the mailbox database fails, your transaction logs will not be lost. Transaction logs are essential to bringing the mailbox database back to a current state after restoring a backup.

Exchange Server 2010 does not have the same disk I/O requirements as previous versions of Exchange, and Microsoft states that you can use low-cost SATA drives. Even so, a stripe set -- preferably with mirroring -- is almost always necessary for the mailbox database in mid-size and large organizations.

Don't take the process of shopping for hardware to run Exchange 2010 lightly. Although Microsoft provides some good guidelines, it is important to consider your own unique needs and to account for any anticipated growth.

Brien Posey is an eight-time Microsoft MVP with two decades of IT experience. Before becoming a freelance technical writer, Brien worked as a CIO at a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the nation’s largest insurance companies and for the Department of Defense at Fort Knox.

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