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Those familiar with Exchange 2003 know that it can be a challenging workload to manage. Proper design of the server, network and storage architecture is critical for proper performance. In particular, careful sizing and configuration of the storage subsystem is essential to address the heavy demands on disk I/O that Exchange 2003 can generate. Even with the most powerful server hardware available, proper performance of Exchange 2003 is often highly dependent on the performance characteristics of the storage design.
The performance characteristics of Exchange 2003 directly correspond to those of the Windows 32-bit architecture and its inherent limitations. Specifically, addressable memory on a 32-bit platform is limited to approximately 4 gigabytes and only 900MB is available for Exchange 2003 database cache. Since reading application data stored in memory is many orders of magnitude faster than reading it from disk storage, applications are typically designed to run “in memory” to the greatest practical extent. Large Exchange 2003 implementations can easily overrun the addressable memory limit, resulting in increased access to disk and degraded performance if the storage subsystem has not been properly designed.
The type of disk I/O generated by Exchange 2003 can influence performance as well. Exchange 2003 was designed to generate highly randomized I/O traffic in very small (4Kb) chunks. If the disk subsystem is not designed to support this particular type of workload, performance can degrade rapidly. Typically, proper storage design for Exchange 2003 deployments focuses on the number of disk spindles required to support the number of I/O operations per second (IOPS) generated by each user. Unfortunately, particularly with modern high-capacity disks, this I/O demand results in more spindles being required than would otherwise be needed based purely on capacity requirements.
In contrast, Exchange 2007 has undergone a number of architectural improvements. Most notably, Exchange 2007 now runs exclusively on 64-bit hardware and requires a supported 64-bit Windows server operating system. This change in architecture allows effectively unlimited memory for Database Buffer Cache, resulting in dramatically reduced disk I/O workloads.
Exchange 2007 has also increased the maximum number of supported mailbox databases to 50, and 50 storage groups. More storage groups allows for more checkpoint depth per user, which also aids in reducing the need to read from disk (by maximizing utilization of dirty pages in memory). I/O specific changes from Exchange 2003 to Exchange 2007 have increased page sizes from 4kb to 8kb, and I/O coalescing has increased from 64kb to 1MB, resulting in larger but fewer writes. The result is that Exchange 2007 performance has improved substantially over its predecessor and Exchange 2007 workloads run extremely well in a VMware virtual machine.
Testing performed by VMware and its partners has demonstrated the viability of running Exchange 2003 with VMware Infrastructure 3. This has been confirmed by customers who have deployed Exchange 2003 in production environments and are benefiting from the operational advantages of a virtualized Exchange infrastructure. Some have virtualized their entire Exchange 2003 environment and carefully designed their infrastructure to accommodate the architectural challenges noted previously. Others have preferred to split their Exchange implementation, limiting virtualization to server roles such as bridgehead servers, SMTP gateways, and infrastructure services such as domain controllers and global catalogue servers.
Exchange 2007, however, is proving to be much easier to deploy and operate than its predecessors. The dynamics of deploying Exchange 2007 are shifting dramatically in ways that align well with the benefits offered by the VMware Infrastructure 3 platform. This shift is a result of advancements in three key areas: 1. Architectural improvements of Exchange 2007 on a 64-bit platform have drastically increased memory utilization and reduced disk I/O load by 50% or more in many cases; addressing many of the shortcomings found in Exchange 2003. With full support for 64-bit Windows virtual machines, these same benefits are realized when Exchange 2007 is deployed on a VMware Infrastructure 3 platform.
2. Advances in server hardware such as dual and quad-core processors, higher memory density, and advances in storage technology are far outpacing the performance requirements of today’s applications, including Exchange. Virtualization becomes an effective way to leverage the full resources of these systems. Recent performance studies have shown unprecedented performance and scalability of up to 16,000 users on a single 64-bit physical server when Exchange 2007 is deployed on VMware Infrastructure 3.
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