How to run 16,000 Exchange mailboxes on ESX
February 27th, 2008 | 
Author: VMware’s Performance Team posted an amazing article this week on the VROOM! blog. 16,000 Exchange Mailboxes, 1 Server not only offers insights on how to configure Exchange 2007 VMs to support large numbers of mailboxes, but it shows that ESX 3.5 and ESX 3i allow applications to utilize hardware resources that exceed the vendor’s recommended maximums in a physical deployment. Although this test was able to squeeze the Exchange 2007 implementation on a single ESX host without degrading the user experience, the technical details of how it was done provides administrators a blueprint to spread the Exchange VMs across multiple ESX hosts and fully leverage ESX Enterprise features.
“We did this test because we have felt for a while that advances in processor and server technology were about to leave another widely-used and important application unable to fully utilize the hardware that vendors were offering. Microsoft has guidelines on what environment works well with Exchange, and a system with more than eight CPUs and/or 32GB of RAM is beyond the recommended maximums.
Hardware vendors are now offering commodity servers with 16 cores
(quad socket with four cores each) and enough memory slots to hold 256GB of RAM. Within a year or two we would expect this to go up even further, with commodity x86 systems being built with 32 cores. Microsoft Exchange deployments
typically work well with the ’scale out’ model, but that causes server proliferation and underutilized hardware, especially as systems get this large. VMware ESX Server allows us to make more effective use of the hardware and improve capacity.”
The post explains the technical specifications of the host hardware, SAN, VMs, and the various Exchange 2007 components. The Microsoft Load Generator was used to simulate user load for a 8 hour period.
“We ran the tests using both ESX Server 3.5 and ESX Server 3i version 3.5 and the performance was the same across both versions. Tests were run with one through eight virtual machines, and even in the eight virtual machine case about half the CPU resources were still available.”
“These tests ran smoothly and demonstrated what we expected. This should come as no surprise. As new hardware becomes available, the scalability of ESX Server allows us to easily make productive use of the additional capacity.”
Many companies currently run large Exchange mailbox servers in a multi-node clustered configuration, and they are reluctant to migrate to VI. This test from VMware helps illustrate that breaking the clusters and migrating back to multiple Exchange Server VMs has performance and capacity advantages. Leveraging DRS and VMotion, Exchange VMs maintain the ability to provide business continuity and high availability when in a virtual environment with many ESX hosts in a VMware cluster.
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