For this reason, the number of vCPUs in a VM should never exceed the number of physical CPU cores on the ESX host. Each vCPU allocated to VMs running on an ESX host must be scheduled on physical cores within the host. Of course the appropriate number of vCPUs depends on many factors, so this is a general guideline. We suggest configuring most Exchange Servers with two to four vCPUs. In the case of Exchange 2007, using four vCPUs instead of one in the VM would have little or no performance benefit. Conversely, going from one to four vCPUs in Exchange 2010 VM can significantly increase performance of the Exchange VM. Exchange 2010 is the first version of Exchange that can benefit from multiple vCPUs in the VM. This will keep you from allocating more memory to VMs than the amount of physical memory on the ESX host. For the best performance, avoid using the memory overcommit feature in ESX. Allocating more memory to your Exchange VMs will reduce the disk load on the ESX host due to a reduction in page swapping. Allocating an appropriate amount of memory to your Exchange virtual servers will ensure good performance on these VMs. This makes the Exchange 2007/2010 significantly more scalable than previous versions.

The additional memory in the VM is used to cache the Exchange Server information.

Exchange 2007/2010 must run on the Windows 圆4 platform because the increased memory capacity of the 圆4 platform allows Exchange 2010 to cache the information stored on disk. If you’re migrating from Exchange 2003, the increased memory requirements will come as quite a shock. An Exchange 2010 (and 2007) installation running the roles of Mailbox, Hub Transport, Client Access and Management Tools requires 16GB of memory to avoid page swapping! As you know, you can allocate a maximum of 255GB to a Virtual Machine (VM) on ESX. Here are some items to consider when virtualizing your Exchange Servers on ESX. Recent research from Gartner’s Burton Group has concluded that “Enterprise production e-mail servers should be deployed virtualized by default (meaning that it should be an exception backed by specific technical considerations when they are deployed on “bare metal”).” While this underscores the benefits of virtualization I mentioned in my previous blog, it would be wise to follow best practices to get the best results.

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