Microsoft Exchange Server 2010 Requirements : Getting the Right Server Hardware (part 2) - Memory Recommendations, Network Requirements

3. Memory Recommendations

As mentioned previously, the advantage that Exchange Server gets out of the x64 architecture is the ability to access more physical memory. Additional physical memory improves caching, reduces the disk I/O profile, and allows for the addition of more features.

Microsoft recommends a minimum of 4 GB of RAM in each Exchange 2010 server. This amount will depend on the roles that the server is supporting. Table 3 shows the minimum, recommended, and maximum memory for each of the server roles.

Although Microsoft's minimum RAM recommendation for any server hosting the Mailbox role is 4 GB, we strongly recommend a minimum of 6 GB. Once you have calculated the minimum amount of RAM that you require for the server, if you are configuring a Mailbox server, you will need to add some additional RAM for each mailbox. This amount will depend on either your user community's estimated message profile or the mailbox size. You should calculate the memory requirement based on not only the usage profile of your users but also the mailbox size; then you will need to take the larger of these two calculations. So, let's start with the amount of memory required based on usage profiles. Table 4 shows the additional memory required based on the number of mailboxes supported. The user profiles were defined previously in Table 1.

Next, let's look at the recommendations based on the mailbox size. Table 5 shows Microsoft's per mailbox memory recommendations for mailboxes of different sizes.

So for example, a server handling a Mailbox server role should have 4 GB of memory plus the additional RAM per mailbox shown in Table 4 or the memory shown in Table 5 (whichever is larger). Let's do the calculations for a simple organization. If the Mailbox server is supporting 1,000 mailboxes and it is estimated that 500 of the users are average (1.75 GB of RAM if assuming 4 MB per mailbox) and 500 are heavy users (2.5 GB of RAM if assuming 6 MB per mailbox), the server should have about 9 GB of RAM. For good measure, we would recommend going with 10 or 12 GB of RAM so that there is additional RAM just in case it is required.

However we perform the additional calculation based on mailbox size, we may arrive at a different amount of RAM. Of the 1,000 mailboxes that this server supports, 400 of these users have an average mailbox size that is in excess of 10 GB, whereas the remainder of the mailboxes average around 6 GB. That would require 4 GB of RAM (400 times 10 MB per mailbox) for the extra large mailboxes and about 5 GB of RAM (600 times 8 MB per mailbox) for the very large mailboxes. That is a total of about 9 GB of RAM.

So in this case, going with at least 10 GB to 12 GB of extra RAM for mailbox caching will definitely be a good design decision. Remember that these RAM estimates are just that: estimates. Additional factors (message hygiene software, continuous replication, email archiving, and so on) may require more or less RAM (usually more) than the calculations and recommendations here. For example, antivirus and antispam software on Mailbox servers can place a significant burden on RAM. Microsoft publishes a storage calculator that can be useful when estimating RAM requirements; see this article on the Exchange Team blog for more information:

4. Network Requirements

With previous versions of Exchange Server, recommending network connectivity speeds was often a gray area because of the variety of networking hardware that most organizations were using. Essentially, not everyone had a Gigabit Ethernet backbone for their servers. Today, however, Gigabit Ethernet is present in most data centers at least for the data center backbone.

So, the recommendation is pretty simple. All Exchange Server 2010 servers should be on a Gigabit Ethernet backbone. Will Exchange 2010 work on a 100Mb or even 10Mb network? Sure, it will, but you will get the best results in even a medium-sized network if you are using Gigabit Ethernet.

In organizations that have put their Exchange server roles onto different Windows servers (physical or virtual), a lot of communication is taking place between the Client Access servers and the Mailbox servers and a lot of communication between the Hub Transport servers and the Mailbox servers. All Exchange server roles should be Gigabit Ethernet.

The majority of the "client-to-server" communication traffic now takes place between the client (usually Outlook) and the Client Access server. But you will still see some MAPI traffic between Outlook clients and Mailbox servers that are hosting public folders (if, of course, you are using public folders).

If you are planning to implement database availability groups (DAGs) between two or more Exchange 2010 Mailbox servers, each server will need a second network adapter installed. The first network adapter will be used for MAPI and MAPI.NET connections while the second adapter will be used for replication. The replication network will be on its own IP subnet and should also have Gigabit Ethernet connectivity to the physical network. In large environments with multiple servers and dozens of databases in a DAG, consider adding additional network adapters that act as replication or MAPI network connections.

If you are planning to put DAG members on a separate physical network (such as across the WAN), the maximum network latency between members cannot exceed 250 milliseconds (ms) and there must be sufficient bandwidth to keep up with the volume of replication traffic.