Applies to: Exchange Server 2010
Topic Last Modified: 2009-11-19
There are many factors to consider when selecting hardware for use by Microsoft Exchange 2010. Three of the most critical factors to consider are choice of processor, amount of memory, and selection of storage. This topic provides guidelines for memory configurations that provide good performance and a strong platform for Exchange Server. For detailed guidance and recommended configurations for processors, see Understanding Processor Configurations and Exchange Performance.
When selecting hardware for Exchange 2010, we recommend that you consider the server maximum memory configuration. Different server architectures have different memory limits. We recommend that you check the following technical specifications of the server to determine the most cost-efficient maximum memory configuration for your servers:
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Memory speed Some server architectures require slower memory modules to scale to the maximum supported amount of memory in a specific server. For example, maximum server memory could be limited to 32 GB with PC3 10666 (DDR3 1333) or 128 GB using PC2 6400 (DDR2 800). You should check with the manufacturer to ensure that the memory configuration target for Exchange 2010 is compatible in terms of speed.
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Memory module size Consider the largest memory module size that the server will support. Generally, the larger the memory module, the more expensive. For example, two 2 GB DDR SDRAM memory modules generally cost much less than one 4GB DDR SDRAM memory module and two 4 GB DDR SDRAM memory modules generally cost much less than one 8GB DDR SDRAM memory module.Make sure the maximum memory module size allows you to meet your target memory requirements for Exchange 2010.
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Total number of memory slots Consider how many memory modules that a specific server will support. The total number of slots multiplied by the maximum memory module size provides the maximum memory configuration for the server. Keep in mind that memory modules must sometimes be installed in pairs.
One caveat with this planning method is that some servers experience a performance improvement when more memory slots are filled, while others experience a reduction in performance. Check with your hardware vendor to understand this effect on your server architecture.
Recommended Memory Configurations
After the number of processor cores estimated to be required per server role is understood, baseline memory recommendations can be applied. The following table illustrates the minimum supported and recommended memory configurations for Exchange 2010 server roles.
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Our recommended memory configuration for the server roles below are a best practice. Also, not that the amount of memory you include for your server roles does not affect your supportability.
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The following describes the minimum requirements and recommended maximum configurations:
Minimum Supported This is the minimum memory configuration suitable for Exchange 2010 servers. The minimum hardware requirements must be met to receive support from Microsoft Product Support Services.
Recommended Maximum This is the recommended memory configuration for multi-role servers. Recommended is defined as the best configuration based on price and performance.
The following table shows the recommended minimum and recommended maximum processor cores for Exchange 2010.
Memory configurations for Exchange 2010 servers based on installed server roles
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Exchange 2010 server role
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Minimum supported
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Recommended
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Edge Transport
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4 GB
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1 GB per core (4 GB minimum)
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Hub Transport
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4 GB
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1 GB per core (4 GB minimum)
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Client Access
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4 GB
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2 GB per core (8 GB minimum)
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Unified Messaging
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4 GB
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2 GB per core (4 GB minimum)
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Mailbox
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4 GB
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4GB plus 3-30MB/mailbox:
This is variable based on the user profile. For more details, see "Mailbox Server Role" section later in this topic.
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Client Access/Hub Transport combo-role (Client Access and Hub Transport roles running on the same physical server)
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4 GB
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2 GB per core (8 GB minimum)
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Multiple roles (combinations of Hub Transport, Client Access, and Mailbox server roles)
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10 GB
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10 GB plus 3-30MB per mailbox (4 core server)
14 GB plus 3-30MB per mailbox (8 core server)
18 GB plus 3-30MB per mailbox (12 core server)
22 GB plus 3-30MB per mailbox (16 core server)
30 GB plus 3-30MB per mailbox (24 core server)
This is variable based on the user profile. For more details, see "Mailbox Server Role" section later in this topic.
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Edge Transport and Hub Transport Server Roles
The Edge Transport and Hub Transport server roles do not require substantial quantities of memory to perform well in optimal conditions. Generally, 1 GB of RAM per processor core (4 GB minimum total) is sufficient to handle all but the most demanding loads. Most deployments will be optimally configured with the recommended memory configuration of 1 GB per processor core (4 GB minimum total).
Client Access Server Role
In general, memory utilization on Client Access servers has a linear relationship with the number of client connections and the transaction rate. Based on the current recommendations of 2GB per core processor and memory configurations, a Client Access server will be balanced in terms of memory and processor utilization, and it will become processor bound at approximately the same time it becomes memory bound.
These recommendations are based on the Exchange 2010 feature, RPC Client Access. This feature requires a larger memory and processor configuration to manage the increase loads placed on the Client Access server role.
Mailbox Server Role
The memory configuration process for the Mailbox server role is more complex than the other roles because the optimal memory configuration depends upon the server roles installed, the mailbox count, the client profile (similar to estimating processor core requirements) and the number of active databases. Memory sizing for the Mailbox server role is critical to reducing disk input/output (I/O) on the server. The more memory you add to the Mailbox server, the less disk I/O that will be generated by Exchange. There is, however, a point of diminishing returns at which adding memory to the server may not be justifiable based on price and performance. The memory recommendations outlined in this section consider this point of diminishing returns, and are based on current memory prices and performance metrics.
For more information about how to perform appropriate memory sizing for the Mailbox Server role, see the following topics:
Multiple Server Roles
When determining memory requirements for multi-role server configurations you need to consider requirements of hub transport, client access, and mailbox server roles. To make this easy, we have provided the calculated memory requirements in the table above. For additional information, see the Memory Recommendations for Multi-Role Servers section in Understanding the Impact of Multi-Role Configurations on Capacity Planning.