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Going 64-Bit with Microsoft Exchange Server 2007

Note on IT

Published: November 30, 2006

Almost two years before the Microsoft Exchange Server product group decided to support Microsoft Exchange Server 2007 only on the 64-bit platform, the Microsoft Information Technology (Microsoft IT) group began to migrate from 32-bit to 64-bit server hardware. All server computers purchased for messaging purposes after the year 2004 are 64-bit systems suitable for Exchange Server 2007. By running the new Exchange Server version on the 64-bit platform, Microsoft IT can keep pace with ever-increasing performance expectations, raise mailbox quotas by up to a factor of 10, lower storage costs, and eliminate tape backups to save an additional $5 million US per year.

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Document Definition

Intended Audience

Products & Technologies

A Note on IT is a short, technically deep drilldown on a specific topic related to Microsoft IT and is usually associated with an existing IT Showcase document. A Note might illustrate how Microsoft IT performs a specific operational task step by step or configures a hardware device or software application. It might also relate details of a best practice or contain key information about Microsoft IT's operations that is regularly requested by customers.

Microsoft Exchange Server 2007 consultants, system administrators, and backup operators.

  • Microsoft Windows Server 2003
  • Microsoft Exchange Server 2003
  • Microsoft Exchange Server 2007
  • AMD64 and EM64T technology
  • Storage area networks
  • Direct-attached storage
  • Redundant array of independent disks (RAID)
  • Windows Clustering
  • Windows Backup program
  • Extensible Storage Engine
  • Cluster continuous replication
  • Transport dumpster

Introduction

During the rollout of Microsoft Exchange Server 2003, Microsoft IT decided to maximize the number of users per mailbox server to facilitate server and site consolidation efforts. Prior to the Exchange Server 2003 rollout, the corporate messaging environment included 118 mailbox servers in 75 locations worldwide. Based on the capabilities of the 32-bit server hardware available at that time, Microsoft IT designed the Exchange Server 2003 mailbox servers for 4,000 users with quotas of 200 megabytes (MB) per mailbox. This design enabled Microsoft IT to realize tremendous cost savings and consolidate the entire messaging environment to just 30 virtual Exchange mailbox servers in four data centers. A fifth data center with Exchange servers exists, but these servers are mail gateways to the Internet that do not store user mailboxes.

Hosting 4,000 users on Exchange Server 2003 servers with 99.99 percent availability made it necessary for Microsoft IT to deploy the mailbox servers in server clusters using the Microsoft Windows Server® 2003 Cluster service. Microsoft IT scaled the original Exchange Server 2003 server clusters up to 16,000 users with four active nodes, one primary passive node, and two secondary passive nodes. The hardware configuration of the primary passive node matched that of the active nodes. In the event of a single-node failure, failover could occur to the primary passive node without performance degradation. With server clusters, Microsoft IT achieved 99.99 percent availability levels, including both unplanned (outages) and planned downtime (maintenance, security updates, and so on). Yet, clustered Exchange Server 2003 servers do not provide redundancies at all system levels. Especially, the Exchange Server databases remained single points of failure.

To protect these databases, Microsoft IT deployed a fault-tolerant, shared storage solution based on high-performance storage area network (SAN) technology. The costs associated with this SAN-based solution and the general limitations on the 32-bit platform prevented Microsoft IT from increasing the number of users per server or the quotas per mailbox in the production environment for the past three years. Nonetheless, the number of users and the demand for larger mailbox sizes increased considerably during this period.

Exchange Server 2007 on the 64-bit platform provides Microsoft IT with new options to respond to the messaging trends and needs that emerged since the rollout of Exchange Server 2003 in the production environment. New Exchange Server 2007 features, such as server clusters without shared storage based on Continuous Cluster Replication (CCR), enable Microsoft IT to eliminate the dependency on SAN technology in the cluster design and start using more cost-efficient direct-attached storage (DAS). The 64-bit platform supports eight Terabytes of user-mode memory and another eight Terabytes of kernel-mode memory. These memory limits practically eliminate all issues related to virtual memory fragmentation or shortage of kernel resources. With such high memory limits, a 64-bit Exchange server has a large pool of system resources available to handle theoretically a very large number of concurrent client connections. The maximum number of concurrent client connections depends to a large degree on the amount of virtual memory (specifically kernel memory) available to the operating system. This one factor can enable IT organizations such as Microsoft IT to provide cost-efficient storage and increased scalability in the production environment.

"The optimizations we have made in Exchange Server 2007 for the 64-bit platform cause the 32-bit platform to perform worse in many cases. Rather than produce two different releases, one targeted to 32-bit and one targeted to 64-bit, we thought it best to keep things focused on one product. We faced a tradeoff of delivering an Exchange Server product that tried to eke out a few dollars of savings on yesterday's architecture, or a product truly optimized for today's modern hardware that will deliver incredible cost savings to our customers."

Terry Myerson
General Manager
Exchange Server Product Group
Microsoft Corporation

This document discusses the most important issues that forced Microsoft IT to stay with 4,000 users and 200 MB quotas on the 32-bit platform. It also describes the important trends and emerging necessities that compel Microsoft IT to increase service levels. The 64-bit platform helps Microsoft IT to accomplish this goal with new architecture limits, such as by supporting larger mailboxes with 2 gigabyte (GB) quotas. In addition, this paper discusses the server designs, including microprocessor choices, random access memory (RAM), and storage configuration, and the backup strategies that Microsoft IT defined for the rollout of Exchange Server 2007.

Note: For security reasons, the sample names of internal resources and organizations used in this document do not represent actual names used within Microsoft and are for illustration purposes only. In addition, the contents of this document describe how Microsoft IT runs its enterprise data center. The procedures and processes included in this document are not intended to be prescriptive guidance on how to run a generic data center and may not be supported by Microsoft Customer Support Services.

Microprocessor and Operating System Developments

Enterprise server technology has evolved since Microsoft IT designed and deployed the original Exchange Server 2003 mailbox servers. Two years earlier, in the year 2001, Intel Corporation launched a 64-bit microprocessor called Itanium. Although Itanium did not bring immediate success because of cost and 32-bit backward compatibility issues, it signaled that PC-based servers could have compelling answers to the reliability, performance, and scalability demands of the enterprise. It is not possible to run Exchange Server on Itanium-based computers, but Microsoft Windows Server 2003, Enterprise Edition for Itanium-based Systems, available since the initial release of Windows Server 2003, enabled Microsoft IT to improve the performance and scalability of database management systems and line-of-business applications, such as Microsoft SQL Server™ and SAP R/3.

The breakthrough came in the year 2003 under the acronym AMD64, when Advanced Micro Devices, Inc. (AMD), introduced the AMD Opteron processor. This microprocessor is fully 32‑bit compatible because its design follows Intel Architecture 32-bit (IA-32, better known as x86). Subsequently, Intel came forward with Extended Memory 64-bit Technology (EM64T), a technology comparable to AMD64. At present, AMD and Intel offer a broad range of x64 microprocessors for entry-level computers and enterprise servers. Both AMD and Intel drive the development forward with multi-core technology. Exchange Server 2007 is the first Exchange Server version that takes full advantage of x64 multi-core microprocessors.

Microprocessors based on x64 support the following two operating modes:

  • Legacy Mode. The microprocessor functions like a 32-bit x86 central processing unit (CPU) with support for 16-bit Real Mode, Virtual-8086 Mode, and Protected Mode. Legacy Mode provides the required backward compatibility for running 32-bit operating systems, such as Microsoft Windows® 2000 Server or 32-bit editions of Windows Server 2003, and 32-bit applications, such as Exchange Server 2003.
  • Long Mode. The microprocessor supports native 64-bit operating systems, such as Windows Server 2003, Enterprise x64 Edition, which Microsoft released along with Windows Server 2003 Service Pack 1. This mode brings all the benefits to Exchange Server 2007 performance. In Long Mode, the microprocessor cannot switch into Real Mode, Virtual-8086 Mode, or Protected Mode, but a Compatibility Mode exists to support native 32-bit applications. For example, Windows Server 2003, Enterprise x64 Edition, uses Compatibility Mode to implement a 32-bit Windows emulation layer, called Windows 32-bit on Windows 64-bit (WoW64). Through WoW64, most 32-bit Windows-based applications can run on 64-bit versions of Windows Server 2003 without code recompilation. However, Exchange Server 2003 cannot run on WoW64 due to driver incompatibilities.

Note: The term x64 generically refers to 32-bit compatible, 64-bit x86 microprocessor architectures based on AMD64 or EM64T.

Limitations on the 32-bit Platform

With 64-bit technologies and improvements in system bus speed, processing performance of servers continues to increase. Exchange Server 2003 benefits from the additional processing power, but it cannot fully exploit the potential because the 32-bit versions of Exchange Server were not designed for the 64-bit platform and cannot run on 64-bit versions of Windows Server 2003. The Exchange Installable File System (ExIFS) uses a 32-bit, kernel-mode driver. A 64-bit compatible ExIFS driver version is not available.

The fact that Exchange Server 2003 does not run on the 64-bit platform makes it difficult to scale up Exchange 2003 servers because:

  • Exchange Server 2003 cannot address more than 4 GB of virtual memory.
  • Kernel-mode memory limits the scalability of the 32-bit versions of the Windows Server operating system.
  • The rate of virtual memory fragmentation increases proportionally with the load (that is, concurrent number of user connections per mailbox server, usage pattern, additional processing such as antivirus scanning or full-text indexing, and other activities).
  • Input/output (I/O) requirements constrain the design of the storage solution. The I/O requirements are high because the virtual memory to cache the data is limited in size. A small cache means Exchange Server reads data from physical disk more often.
  • Backup speed and throughput limit the amount of data that mailbox servers can maintain. With Exchange Server 2007, Microsoft IT can implement an entirely revised high availability and backup solution based on Continuous Cluster Replication (CCR) and Microsoft Data Protection Manager Version 2. CCR is not available in Exchange Server 2003.

Note: Running a 32-bit version of the Windows Server operating system on 64-bit server hardware does not increase the operating system's scalability. Consequently, Microsoft IT decided to keep the ratio of 4,000 users per server with quotas of 200 MB per mailbox for Exchange Server 2003 in place, even after the arrival of x64-based hardware in the data centers.

Physical and Virtual Memory Limitations

The address registers of a 32-bit microprocessor are traditionally 32 bits wide, limiting the physical address space of RAM to 4 GB (232 bytes = 4294967296 bytes = 4 GB). Although Intel extended the address registers with Intel Pentium Pro and later microprocessors from 32 bits to 36 bits to increase the address space to 64 GB (236 = 64 GB), and even though the x64 architecture could theoretically reference 16 exabytes of memory with 64-bit addresses, x64 microprocessors in Legacy Mode continue to use an address size of 32 bits and do not support memory extensions. The 32-bit versions of the Windows Server operating system that Exchange Server 2003 requires run in Legacy Mode on x64 microprocessors. Therefore, equipping a computer running Exchange Server 2003 with more than 4 GB of RAM does not provide advantages.

Addresses that are 32 bits in size also imply that the Windows Server operating system can provide only 4 GB of virtual memory to each running application. Yet, the entire 4 GB may not be available to the user-mode process (the application). In the default configuration, the operating system reserves the upper 2 GB for system data structures and kernel-mode components, such as device drivers, leaving only the lower 2 GB for the 32-bit application. This ratio can be changed by adding the /3GB startup parameter to the Boot.ini file, which causes Windows Server 2003 to limit the kernel-mode memory to 1 GB and to extend the user-mode memory to 3 GB. This is the absolute maximum. Exchange Server 2003 cannot use more than 3 GB of virtual memory regardless of the amount of physical memory installed.

Note: Current x64 microprocessor implementations use a 40-bit address bus to support a maximum of one Terabyte of physical memory. The current x64-based versions of Windows Server 2003 use 44-bit addresses, which amounts to 16 Terabytes of virtual memory (eight Terabytes for the kernel and eight Terabytes for the user-mode process). Exchange Server 2007 is the first Exchange Server version that can exploit this potential.

Kernel-Mode Memory Issues

The kernel is the core of the operating system. The kernel is responsible for security, low-level I/O operations, process management, thread scheduling, interrupt handling, memory management, device drivers, and more. It encapsulates the hardware resources on top of the hardware abstraction layer (HAL) and provides system services that the user-mode processes require. To perform its tasks, the kernel needs memory for crucial resources, such as for boot and system drivers, system page table, file system cache, paged pool, and non-paged pool. This kernel-mode memory can be an overriding scalability factor on the 32-bit platform.

The /3GB switch limits kernel-mode memory to 1 GB and reduces the size of the kernel's memory pools considerably. For example, the size of the non-paged pool decreases from 256 MB to 128 MB. This is a critical issue because it reduces the number of concurrent client connections that the server can handle. Among other things, every TCP/IP connection requires the kernel to allocate memory from the non-paged pool. The various kernel-mode components in the network stack use this memory for buffering of data structures during send and receive operations. The data must stay resident in memory because the processing of interrupt requests from a network adapter cannot tolerate page faults. The ExIFS kernel-mode driver of Exchange Server 2003 also uses non-paged memory to read and write items to and from the messaging databases.

In addition to the non-paged pool, the paged pool represents a limiting factor as well. The paged pool is memory that the kernel can swap to the page file on disk. Device drivers and other kernel-mode components can use the paged pool for system resources. For example, the IP security (IPsec) device driver uses paged pool memory to maintain security associations. The Configuration Manager in Windows Server 2003 uses the paged pool to store file-mapping objects to access the configuration data in the Windows registry database. The security subsystem of Windows Server 2003 also uses paged pool memory to store access tokens for every user session, which contain security IDs (SIDs) to determine access levels to system resources for users and groups. With the /3GB switch, the default size of the paged pool drops from 356 MB to just 256 MB, and with it drops the maximum number of client sessions (such as Office Outlook® 2003 clients) that the server can sustain.

Microsoft IT experienced this session limitation on its large-scale Exchange Server 2003 mailbox servers. Connectivity issues were noticeable when a large number of Microsoft Office Outlook 2003 and other messaging clients established connections, such as on Monday mornings between 09:00 and noon (which is a typical peak-load period at Microsoft). Error events in the mailbox servers' system event logs indicated paged pool allocation failures. Microsoft IT determined that the large number of concurrent sessions (including Office Outlook 2003 in cached mode and online mode, Microsoft Office Communicator, and other types of client connections), caused the kernel to exhaust the paged pool by generating an average of eight copies of each user's access token per client. Microsoft confirmed this to be an issue and provided a hotfix for the Microsoft Exchange Information Store (Store.exe), publicly documented at http://support.microsoft.com/kb/912480/. The hotfix mitigates the issue by reducing the number of tokens required per client session, but the limitations of the 32-bit platform remain because the sizes of the paged pool and non-paged pool do not increase.

Note: Kernel-mode memory limitations are not an issue for Exchange Server 2007 on the 64-bit platform because Windows Server 2003, Enterprise x64 Edition, provides eight Terabytes of virtual memory for the kernel. The address spaces for paged pool and non-paged pool in virtual memory are each 128 GB in size. For detailed information, see the Microsoft Knowledge Base article "Comparison of 32-bit and 64-bit memory architecture for 64-bit editions of Windows XP and Windows Server 2003" available at http://support.microsoft.com/kb/294418/.

Virtual Memory Fragmentation

In addition to kernel-mode memory limitations, another issue that Microsoft IT encountered in the production environment has its cause in the fragmentation of virtual memory that occurs over time on large mailbox servers when processes intensively allocate and de-allocate virtual memory. Especially, processes that use small memory chunks in large quantities can promote virtual memory fragmentation.

For example, the Extensible Storage Engine uses scatter-gather I/O operations to read data from the messaging databases, spreading the data in a single operation over non-contiguous memory pages. It is no coincidence that Exchange Server 2003 organizes the data inside the database file sequentially in a balanced tree (B+ tree) of database pages each 4096 bytes in size. At 4096 bytes, a database page fits exactly into one memory page. However, ESE must use virtual memory very carefully because scattered memory pages can lead to a situation where the free space between the individual memory pages is too small to be useable for other processing tasks. This is less of an issue on the 64-bit platform because eight Terabytes of user-mode memory provide substantially more free space than two or three GB of user-mode memory on the 32-bit platform. Yet, on the 32-bit platform, virtual memory fragmentation is a scalability-limiting concern.

To understand the impact on the 32-bit platform, it is important to know that virtual memory allocation works only with contiguous address blocks. For example, the Exchange Information Store process needs approximately 10 MB of memory to control a storage group and mount its databases. Yet, if the largest available free block of virtual memory is fewer than 10 MB in size, mounting databases fails because Store.exe cannot allocate the required memory no matter how many smaller chunks are available.

Although the largest available contiguous address block may be of significant size when the Exchange Information Store process starts, it is typical to see a considerable decline when Store.exe allocates and frees memory during processing. At Microsoft, on 32-bit mailbox servers with 4,000 mailboxes, the largest free virtual memory block is sometimes only 200 MB in size. On extremely busy Exchange Server 2003 servers, the largest available coherent memory block might even drop below 32 MB, causing performance and stability issues.

If the free coherent space drops below 16 MB, message processing can fail, performance can degrade severely, and unexpected system behavior can occur. In this situation, restarting the Exchange Server services is unavoidable to reinitialize the virtual memory and bring the server back into an operational state. For more information, see the Knowledge Base article "How to Troubleshoot Virtual Memory Fragmentation in Exchange Server 2003 and Exchange 2000 Server" at http://support.microsoft.com/kb/325044.

Input/Output Operations

The limited availability of virtual memory on the 32-bit platform also has a direct impact on input/output (I/O) operations because even under the best theoretical circumstances, the Exchange Server 2003 Information Store process cannot load more than 3 GB of data from the databases into virtual memory for processing at any given time. Data processing requires the data to reside in virtual memory. If 4,000 users concurrently access the mailbox server, the Exchange Information Store process can use only about 800 KB per user. This is a very theoretical calculation because Store.exe does not provide all users with an equal amount. If a particular request requires more memory for processing, the Exchange Information Store process discards other data to free virtual memory. This implies that the storage engine has to keep reloading frequently used data, such as system tables and indexes, which it has to evict whenever other requests require the memory space. Accordingly, I/O activities on a large Exchange Server 2003 mailbox server are very high.

In reality, the amount of virtual memory that is available to the storage engine on the 32-bit platform is much lower than 3 GB because loading the program code already consumes memory and the Exchange Server 2003 Information Store process needs virtual memory for other processing tasks as well, such as for maintaining storage groups and databases. By default, the Exchange Information Store process allocates only between 576 MB (without the /3GB startup parameter) and 896 MB (with the /3GB startup parameter) for the Store Database Cache, also called the Jet cache or ESE buffer. The maximum configurable value is 1,200 MB. Regardless of database sizes, this is the maximum amount of virtual memory that the storage engine can depend on to perform its read and write operations on the 32-bit platform. On Microsoft IT's mailbox servers supporting 4,000 users, this limitation implies that, on average, Exchange Server 2003 with /3GB startup parameter could only use approximately 230 KB of ESE buffer per user (896 MB / 4,000 users = ~230 KB/user).

Note: The limited availability of memory on the 32-bit platform remains an issue that only the 64-bit platform can solve. In Exchange Server 2007, the Exchange Information Store process adjusts the ESE buffer dynamically according to the amount of physical memory installed. For example, on a 64-bit server for 4000 users with 24 GB of physical memory, the Exchange Information Store process uses up to 20 GB of virtual memory for the ESE buffer. The storage engine can load approximately five megabytes instead of a few hundred kilobytes per user from the databases and can cache that data longer, which results in a decrease of I/O operations by as much as 70 percent in comparison to the 32-bit platform.

Input/Output and Storage Requirements

To clarify the I/O requirements on the Exchange Server 2003 mailbox servers, Microsoft IT monitored the Disk Transfers/sec, Disk Reads/sec, and Disk Writes/sec performance counters over a period of several weeks during the initial deployment phase. Based on the performance statistics, Microsoft IT determined that its Exchange Server 2003 servers with 4,000 mailboxes must be able to perform approximately 3,200 reads and 1,600 writes per second during peak loads, which amounts to 1.2 I/O operations per second (IOPS) per user. This is a Microsoft-specific result. The I/O requirements are relatively high because Microsoft employees are power users and internal business communication relies heavily on e-mail messaging. Exchange servers in other organizations will have different I/O requirements. It is also noteworthy that the performance capacity increased with Exchange Server 2003 Service Pack 1. I/O dropped on Microsoft IT mailbox servers from 1.2 to 0.9 IOPS per user.

Note: Microsoft IT measures disk throughput in the form of IOPS per user. At 3,200 reads and 1,600 writes for 4,000 users, the system must perform 1.2 IOPS per user according to the following calculation: 3,200 + 1,600 = 4,800 / 4,000 = 1.2. The storage subsystem must not only provide this I/O throughput, but also ensure acceptable read and write latencies for Exchange Server transactions.

For the original Exchange Server 2003 server cluster design, to meet the performance and redundancy requirements of the shared storage subsystem, Microsoft IT deployed an expensive SAN-based solution. For each mailbox server, Microsoft IT configured stripe sets of mirrored drives according to redundant array of independent disks (RAID) level 1+0 (also called RAID 10). The high-performance fibre channel disks that Microsoft IT used operated at 10,000 revolutions per minute (RPM) and were able to carry out 130 physical data transfer operations per second during random Exchange database operations while providing acceptable read latencies below 20 milliseconds (ms). This meant that the storage solution for the database drives required 48 hard disks. The requirement calculation assumed 3,200 reads and 1,600 writes per second during peak loads. In a RAID 10 configuration, this results in 6,400 data transfers per second to the disks because each write operation arriving at the host bus controller translates into two writes that the array controller must perform (3,200 + 2 × 1,600 = 6,400). At 130 data transfers per second, 49 disks are required to provide the necessary throughput (6,400 / 130 = ~49). Microsoft IT used an even number of 48 disks according to RAID 10 requirements.

Backup Dependencies

The SAN-based solution that Microsoft IT decided to use for Exchange Server 2003 mailbox servers provided 12 Terabytes of raw disk capacity. Nevertheless, Microsoft IT had to limit the mailbox capacities based on 200 MB quotas. This represented a 100 percent improvement over Microsoft Exchange 2000 Server conditions with 100 MB mailbox quotas. Yet, one factor that prevented Microsoft IT from setting the quotas even higher was backup performance.

For a server cluster that supports 16,000 users, a quota of 200 MB per mailbox with a deleted items retention time of three days signifies approximately 4.5 Terabytes of data. The individual mailbox servers had to each maintain approximately 1.2 Terabytes of data in the mailbox databases. Although Microsoft IT developed a solution to complete backups in less than four hours, a further increase of mailbox numbers or capacities was not sustainable because Exchange Server 2003 also requires time for online database maintenance. Completing online maintenance cycles regularly is critical to keep the Exchange server healthy, the system performance stable, and the sizes of database files under control. Because the server requires time for online maintenance, Microsoft IT did not extend the time window for daily backup operations (disk-to-disk) beyond four hours, which is a limiting factor for mailbox capacities.

Table 1 shows the backup and maintenance schedule that Microsoft IT established for the Exchange Server 2003 mailbox servers in Redmond, Washington.

Table 1. Workload Pattern for Exchange Server 2003 Mailbox Servers

Operation

Starts

Ends

Comments

Production

05:00

20:00

The production period starts at 05:00 to accommodate users in other time zones in the United States, such as Eastern Time (US & Canada).

Backup

20:00

24:00

The four-hour backup window starts at 20:00. The backup operation is consistently complete around 23:30.

Online maintenance

02:00

05:00

Following the backup operation and a period of inactivity for two hours, online maintenance begins. Online maintenance stops on weekdays at 05:00 and at 09:00 on weekends and resumes the next day. Microsoft IT strives to complete the maintenance cycle at least once a week across all store databases per mailbox server.

Messaging Trends and Needs

The statistics that Microsoft IT gathered in the corporate environment confirm that e-mail communication continues to grow in importance and volume at Microsoft. The mailbox count grew by approximately 75 percent over the past five years, and mobile clients (Exchange ActiveSync®) multiplied by a factor of five. Messages received on a daily basis from the Internet have increased continuously. Moreover, messages include more and more rich content—developments that continue to accelerate with the broadened deployment of Unified Messaging.

Table 2 illustrates the growth in e-mail communication over five fiscal years at Microsoft.

Table 2. Microsoft Messaging Statistics and Projections

Category

2002/2003

2003/2004

2004/2005

2005/2006

2006/2007

Mailboxes total

71,000

80,000

95,000

110,000

130,000

Exchange ActiveSync users per month

Not applicable

6,000

13,000

21,000

31,000

Outlook over remote procedure call (RPC)/Hypertext Transfer Protocol (HTTP) per month

Not applicable

20,000

25,000

60,000

60,000

Internet message submissions per day (unfiltered)

6,000,000

9,000,000

11,300,000

13,000,000

13,500,000

Blocked message submissions per day

2,500,000

7,500,000

10,000,000

10,500,000

11,000,000

Maximum message size

2 MB

5 MB

10 MB

10 MB

10 MB*

E-mail volume per user per day

10 MB

15 MB

15 MB

20 MB

25 MB

Number of mailbox servers

113

38

34

30

62

Typical mailbox quota

100 MB

200 MB

200 MB

200 MB

500 MB or 2 GB

Total mailbox data

7 Terabytes

17 Terabytes

19 Terabytes

22 Terabytes

Up to 260 Terabytes

* Size will increase after completion of Exchange Server 2007 migration

Storage capacities must increase to keep pace with the trends. It is crucial for Microsoft IT to provide users with larger mailboxes because corporate management encourages employees to stop using personal folders to archive their messages. Currently, users can download messages to personal folders on their local computers when their mailboxes reach the capacity limit. In the future, however, after Microsoft IT deactivates support for personal folders in the production environment, this option will no longer be available. It will be imperative to provide sufficient storage capacity on the mailbox servers so that users can keep all their important messages for as long as the messages are relevant and needed. Through surveys and during pilot projects, Microsoft IT determined that depending on job responsibilities, users would require mailbox capacities of between 500 MB and 2 GB to maintain their productivity levels.

Note: Following the deployment of Exchange Server 2007, Microsoft IT plans to deactivate write access to personal folders through Group Policy settings by using the DisablePSTGrow registry parameter. Read-only access enables users to retain archived messages on local computers. However, all new messages must remain on the server. At that time, the mailboxes at Microsoft will grow in size.

Exchange Server 2007 Deployment Goals

In preparation for the production deployment, Microsoft IT performed lab tests and pilot rollouts by using the beta versions of Exchange Server 2007. Beta 2 showed considerable improvements in I/O performance over previous Exchange Server versions. IOPS per user dropped from 0.9 on servers running Exchange Server 2003 SP1 to a value of 0.27 on servers running Exchange Server 2007 at Microsoft, which meant that Microsoft IT could support an increased number of users per Exchange Server 2007 mailbox server, higher quotas per mailbox, or both.

Microsoft IT decided to focus on increasing mailbox quotas up to 2 GB. To complete the migration of 130,000 users in less than three months and before the product's release to manufacturing (RTM), Microsoft IT decided to place between 2,400 and 3,600 users with mailbox quotas of 500 MB on the majority of the mailbox servers. Following the successful completion of the project, Microsoft IT will increase the quotas in North America to 2 GB. At that time, Microsoft IT may also decide to increase the number of users per server. However, during the migration, maximizing the number of users per server was not a priority.

Server Roles and Server Hardware

In the Exchange Server 2003 production environment, Microsoft IT deployed almost exclusively dedicated front-end servers, gateway servers, hub servers, public folder servers, and mailbox servers for the reasons of performance and capacity planning. Most of these server types translate directly to corresponding counterparts in Exchange Server 2007. Microsoft IT will replace front-end servers with Client Access servers, Internet mail gateway servers with Edge Transport servers, hub servers with Hub Transport servers, and public folder and mailbox servers with the Exchange Server 2007 Mailbox server role. There is also one role in Exchange Server 2007 without a counterpart in previous versions, the Unified Messaging server. Prior to Exchange Server 2007, Microsoft IT used a third-party solution for unified messaging, which Microsoft IT replaced with Voice over IP (VoIP) gateways and Exchange 2007 Unified Messaging servers.

Advantages of Server Roles

A deployment of dedicated servers based on roles provides Microsoft IT with the following advantages.

Structured System Administration and Maintenance

At Microsoft IT, many groups deploy and manage the messaging environment. All groups collaborate closely, while various system engineers, program managers, and service managers maintain different aspects of the messaging environment. Structured collaboration according to server roles enables each member on the Exchange messaging team to focus on specific areas of expertise.

Optimized Server Hardware and Software Components

The server roles have specific purposes and perform different tasks, placing various requirements on hardware and software components. For example:

  • Client Access servers. Perform message conversions and support Internet mail clients, Exchange ActiveSync clients, Office Outlook Web Access, and Outlook Anywhere.
  • Edge Transport servers. Handle all message traffic to and from the Internet and run spam filters and antivirus scanners.
  • Hub Transport servers. Perform the internal message transfer, distribution list expansions, and message conversions between Internet mail and Exchange Server message formats, as well as enforce message policies.
  • Mailbox servers . Maintain the public folder and mailbox store databases and provide Office Outlook clients and Client Access servers in the internal network with access to the data.
  • Unified Messaging servers. Communicate with Private Branch Exchange (PBX) switches and VoIP gateways to integrate voice messaging services into the messaging environment. Unified Messaging servers also run Outlook Voice Access to support mobile users.

Microsoft IT chose a different hardware configuration for each server role, as shown in Table 3 later in this Note on IT.

Targeted Load-Balancing and Clustering

The use of load-balancing and clustering technologies depends on the role that the server assumes in the messaging environment. For example, Microsoft IT uses Windows Clustering to increase the availability of Mailbox servers. For Edge Transport servers, Microsoft IT uses Domain Name System (DNS) round robin. Hub Transport servers do not require an explicit load-balancing solution because the Mail Submission Service of Exchange Server 2007 automatically balances the load between multiple Hub Transport servers if they are available in the local Active Directory® domain service site. For Client Access servers, Microsoft IT uses Network Load Balancing (NLB). For Unified Messaging servers, Microsoft IT load balances at the VoIP gateway level.

Increased Flexibility in the Messaging Environment

Through continuous system monitoring by means of Microsoft Operations Manager (MOM), Microsoft IT can quickly detect bottlenecks and other issues. Because the servers perform dedicated tasks, Microsoft IT can isolate problem sources faster than would be possible on servers with a broader scope. Dedicated servers also enable Microsoft IT to accommodate future demand more directly. For example, if the number of mobile users continues to increase at Microsoft (as the trends indicate), Microsoft IT can deploy additional Client Access servers without affecting Mailbox or Hub Transport servers.

Server Hardware Configurations

It is important to note that Microsoft IT designed its Exchange server hardware during the Exchange Server 2007 Beta 1 and Beta 2 timeframe. Yet, the beta versions of Exchange Server 2007 did not contain all performance optimizations. The Release to Manufacturing (RTM) version contains the complete, optimized code that places a reduced demand on server hardware. In other words, the selected hardware discussed in this paper may be more than sufficient for running the RTM version of Exchange Server 2007.

As shown in Table 3, Microsoft IT strives to use similar hardware configurations and storage designs per Exchange Server 2007 server role. This facilitates maintenance and supports a high degree of deployment automation based on Windows PowerShell scripts and unattended installations. Even the different categories of Exchange Server 2007 Mailbox servers that Microsoft IT decided to deploy rely on similar storage configurations and drive letter assignments. The Mailbox I category supports 2,000 users with 500 MB mailbox quotas, Mailbox II supports 2,400 users with 2 GB mailbox quotas, and Mailbox III supports 3,600 users with 2 GB mailbox quotas.

Table 3. Server Hardware per Server Role

Server role

Processors

Memory

Raw Storage Capacity

Client Access

Two dual-core
AMD Opteron
2.2 GHz

4 GB

50 GB for the operating system

20 GB for miscellaneous data (tools, temp files, dumps, and so forth)

70 GB for Exchange Server and Internet Information Services (IIS) files

Edge Transport

Two dual-core
AMD Opteron
2.2 GHz

8 GB

50 GB for the operating system

20 GB for transaction log files for queue database

275 GB for queue database files, tracking logs, protocol logs, Exchange binaries, and similar files

Hub Transport

Two dual-core
AMD Opteron
2.2 GHz

8 GB

50 GB for the operating system

20 GB for transaction log files for queue database

275 GB for queue database files, tracking logs, protocol logs, Exchange binaries, and similar files

Mailbox I

(2,000 users with 500 MB quotas)

Two dual-core
Intel Xeon
2.66 GHz

12 GB

50 GB for the operating system

96 GB for Exchange Server binaries

730 GB for maintenance and recovery

584 GB for transaction log files

2,336 GB for database files

5,000 GB for backup files

Mailbox II

(2,400 users with 2 GB quotas)

Two dual-core
Intel Xeon
3.0 GHz

16 GB

50 GB for the operating system

250 GB for Exchange Server binaries

900 GB for miscellaneous data

1,800 GB for transaction log files

7,200 GB for database files

7,000 GB for backup files

Mailbox III

(3,600 users with 2 GB quotas)

Four dual-core
AMD Opteron
2.6 GHz

24 GB

50 GB for the operating system

250 GB for Exchange Server binaries

900 GB for miscellaneous data

2,700 GB for transaction log files

10,800 GB for database files

14,000 GB for backup files

Unified Messaging

One dual-core
AMD Opteron
2.2 GHz

4 GB

50 GB for the operating system

20 GB for miscellaneous data

70 GB for Exchange Server files

Microprocessor Choices

Exchange Server 2007 runs on AMD64-based and EM64T-based microprocessors, such as AMD Opteron, AMD Athlon, Intel Xeon, or Intel Pentium D CPUs. As indicated earlier in Table 3, the production servers use Intel Xeon and AMD Opteron. Specifically, Microsoft IT uses the following processor models that were available in the second quarter of 2006:

  • AMD Opteron model 885 2.6 GHz. Microsoft IT designed the servers in the Mailbox III category during the Exchange Server 2007 Beta 1 phase. Four dual-core AMD Opteron 2.6 GHz microprocessors provided the necessary processing power that Microsoft IT needed to support up to 3,600 users per mailbox server with a mailbox quota of 2 GB.
  • Intel Xeon 5160 3.00 GHz. With the availability of Xeon microprocessors based on the new Intel Core architecture in July 2006, Microsoft IT was able to finalize the Mailbox II server design. Microsoft IT uses two dual-core Intel Xeon 5160 3.00 GHz to support up to 2,400 users per mailbox server with a mailbox quota of 2 GB.
  • Intel Xeon 5150 2.66 GHz. In the Mailbox I design, Microsoft IT is planning to use Intel Xeon 5150 2.66 GHz. The Xeon 5160 is faster than the Xeon 5150, but the Xeon 5150 has roughly 20 percent lower power requirements (65 Watts vs. 80 Watts). For this reason, Microsoft IT chose two dual-core Intel Xeon 5150 2.66 GHz to support 2,000 users per mailbox server with a mailbox quota of 500 MB.

Microsoft IT selected dual-core microprocessors for all mailbox server designs, each of which combines two independent CPUs into a single chip. This is advantageous for multithreaded applications, such as Exchange Server 2007. Multiple cores can run multiple threads concurrently. Lab tests showed a performance increase of approximately 90 percent in comparison to single-core chips, which translates into a better price/performance ratio, reduced power consumption, and lower heat generation.

Random Access Memory Configuration

Microsoft IT configured the system memory for Exchange Server 2007 based on performance tests and according to information from the product development group. To ensure an appropriately sized database cache and an optimum I/O performance on mailbox servers, Microsoft used the following formula to determine the optimal memory requirements for the production mailbox servers: 2 GB + 5 MB per user. For the other server roles, Microsoft IT selected the memory configuration to support increased scalability and performance requirements in the messaging infrastructure.

"The storage engine of Exchange Server 2007 provides performance and reliability at unprecedented levels. By allocating large amounts of RAM for the ESE buffer, we can cache frequently used data, such as the top 50 items in the Inbox, longer for all users. By supporting up to 50 storage groups per server, we can handle write operations very effectively. By increasing the database page size from 4,096 bytes to 8,192 bytes, we can store more data in a single page in the database. Research shows that approximately 75 percent of all messages are smaller than 8 KB, which means we can store message header and body in a single page instead of two pages. An 8-KB page size also means shorter B+ trees in the database, which result in less I/O overhead to get to the pages that store the actual user data. We also removed the streaming database and the ExIFS driver to eliminate expensive switching between kernel mode and user mode. We have reduced the size of the transaction log files from 5 MB to 1 MB to support the new continuous replication features, and I could go on with bit error correction and other features. Let me just say that I am proud of our accomplishments because they translate directly into reduced storage costs, peak performance, and high reliability for our customers."

Chris Mitchell

Software Design Engineer

Exchange Integrated Systems Engineering

Microsoft Corporation

Table 4 compares the minimum product recommendation with the configuration that Microsoft IT selected.

Table 4. Memory Configuration per User Count

Server type

Number of users

Quota per mailbox

Minimum RAM

Microsoft IT RAM

Client Access

Not applicable

Not applicable

1 GB

4 GB

Edge Transport

Not applicable

Not applicable

1 GB

8 GB

Hub Transport

Not applicable

Not applicable

1 GB

8 GB

Mailbox I

2,000

500 MB

12 GB

12 GB

Mailbox II

2,400

2 GB

14 GB

16 GB

Mailbox III

3,600

2 GB

20 GB

24 GB

Unified Messaging

Not applicable

Not applicable

1 GB

4 GB

Microsoft IT considered two main aspects for the memory configuration. The first aspect was the number of mailboxes on the server. For example, with 24 GB of RAM on the largest mailbox servers, the storage engine can use approximately 20 GB for the Extensible Storage Engine (ESE) buffer. This corresponds to about 5 MB per mailbox, which is sufficient to cache the Inbox folder view for the top messages, most calendar items, contacts, and any message-processing rules for each user. The less often ESE needs to reload this information, the better the I/O performance.

The second aspect was storage group count. Microsoft IT designed the Mailbox I and Mailbox II server types for 28 storage groups and the Mailbox III server type for 42 storage groups. Each storage group contains a single mailbox store database. This configuration is required for CCR. In addition, this configuration benefits transaction handling because the storage engine can now cache more data per user for efficient batch processing of write operations—another considerable I/O benefit.

To understand why the storage group count is an important design factor in Exchange Server 2007, it must be noted that ESE maintains transaction log files per storage group in addition to database files to ensure the atomicity, consistency, isolation, and durability (ACID) of all transactions. This means that the storage engine writes all data to disk twice. First, ESE writes the data to the transaction logs. This I/O is sequential and handled most efficiently with caching disk controllers. Yet, the second write operation against the actual database file is expensive because of the random nature of the database I/Os.

To optimize performance, ESE delays the second write operation. The data is safe in the transaction logs and will not be lost, even in the event of a system crash. If necessary, ESE replays the transaction logs at the next start of the Exchange Information Store process. However, by delaying the second write operation, ESE can perform writes in batches and perhaps even eliminate unnecessary writes if the data changes frequently. For example, if data not written to the database changes and must be written again, ESE saves an I/O operation.

Yet, delayed writes require a means to maintain the synchronicity between the transaction logs and the database file. ESE uses checkpoints to maintain synchronicity by checking for the data already written to the database file up to the checkpoint. The checkpoint depth refers to the amount of data that ESE still has to write. By default, the maximum checkpoint depth per storage group is 20 MB. In other words, ESE can keep the data corresponding to up to 20 transaction log files per storage group cached in memory (transaction logs of Exchange Server 2007 are 1 MB in size).

By configuring a separate storage group for each mailbox store database, Microsoft IT maximizes the total checkpoint depth across the entire mailbox server. For example, at 42 storage groups, the total checkpoint depth is 840 MB. Exchange Server 2007 supports a maximum number of 50 storage groups—a total checkpoint depth for the server of 1 GB.

System Drive and Page File

Microsoft IT places the system drive with a size of 50 GB consistently on the first logical disk in all Exchange servers. This placement offers sufficient capacity for the binary files of Windows Server 2003 and the page file, which the operating system uses to swap memory. Windows Server 2003, Enterprise x64 Edition, requires a minimum of 4 GB of disk space. The size of the page file should be equal to the amount of RAM in the server plus 10 MB.

For example, on a mailbox server with 24 GB of RAM, operating system and page file consume approximately 30 GB. Microsoft IT leaves the remaining disk space on the system drive available for service pack updates and other maintenance tasks.

Mailbox Server Storage Design

With Exchange Server 2007 and the 64-bit platform, Microsoft IT is able to design server storage for capacity without being constrained by IOPS. On prototype mailbox servers running Exchange Server 2007 Beta 2, Microsoft IT measured I/O requirements per user in the range of 0.27 IOPS. Furthermore, the read/write ratio changed in comparison to Exchange Server 2003. On the 32-bit platform, the read/write ratio was two reads to one write operation (2:1). Yet, Exchange Server 2007 can use a much larger ESE buffer, caches data longer, delays write operations better to avoid repeated writes to the same object on disk, and uses database pages that are 8 KB in size. These changes affect the read/write ratio. Using Exchange Server 2007 and 2 GB + 5 MB of memory per user, Microsoft IT measured a read/write ratio of 1:1 on mailbox servers. These test results on prototype servers matched the performance information from the product development group.

The following sample calculation illustrates the significance of these improvements. On a server with 4,000 users, 0.27 IOPS per user result in 1,080 I/O operations per second. Using a read/write ratio of 1:1, this means 540 reads and 540 writes. In a RAID 10 configuration where the RAID controller must perform two data transfers to disk for every write operation, the result is 1,620 transfers per second behind the controller (540 + 2 × 540 = 1,620). Microsoft IT uses serial-attached SCSI (SAS) or fibre-channel disks that can perform 130 transfers per second (Large Form Factor, LFF) or 170 transfers per second (Small Form Factor, SFF). Only twelve LFF disks (1,620 / 130 = ~12) or ten SFF disks (1,620 / 170 = ~10) are necessary to deliver the required I/O performance for 4,000 users. The Exchange Server 2007 storage solution does not need to use small disks in great numbers to achieve the required I/O throughput.

Storage Capacity Requirements

For Microsoft IT mailbox servers running Exchange Server 2007, the actual storage capacity needs determine the storage configuration according to the number of users per server with mailbox quotas of 500 MB (Mailbox I) or 2 GB (Mailbox II and III). Microsoft IT uses 146 GB and 300 GB disks based on SAN or DAS. Microsoft IT also uses 500 GB disks, but not for the database or translation log drives. RAID arrays with 500 GB disks implement the backup drives needed for streaming disk-to-disk backup operations, as explained later in this paper.

Microsoft IT determined the storage needs for Exchange Server 2007 mailbox servers based on the following key factors.

Number of Mailboxes and Size Limits

Multiplying the number of mailboxes by the maximum supported mailbox size provides an estimate of the amount of data that the users can store on the server. Although Exchange Server 2007 supports single-instance storage to use database space efficiently, Microsoft IT does not consider this feature in the calculation of database sizes.

Single-instance storage is effective when message recipients reside in the same mailbox store database, yet Microsoft IT uses a large number of mailbox store databases with only a relatively small number of users in each. Hence, it is reasonable to assume that a server with 2,000 mailboxes and quotas of 500 MB must be able to store at least 1 Terabyte of mailbox data in the databases (2,000 × 500 MB = ~1 Terabyte).

Deleted Items Retention

Deleted items retention is an Exchange Server feature that enables users to recover accidentally deleted items directly from within their Outlook clients. For a defined period, the Exchange Information Store retains deleted items for this recovery purpose, and this requires storage space.

At Microsoft, the deleted items retention time is 14 days. Each user, on average, receives 25 MB of e-mail messages every day. Assuming that the user deletes 100 percent of the messages eventually, the mailbox store must be able to retain 350 MB per user (14 × 25 MB = 350 MB). On a server with 2,000 mailboxes, this amounts to an additional 700 GB of data in the mailbox stores (2,000 × 350 MB = ~700 GB). Expressed in percent, 350 MB of additional data per user with a mailbox quota of 2 GB amounts to an additional capacity requirement of approximately 17 percent (350 MB * 100% / 2048 MB = ~17%). To simplify the calculation, Microsoft IT uses a factor of 20 percent for the database overhead.

Context Indexes

Content indexing is enabled by default in Exchange Server 2007 so that users can perform full-text searches of messages and message attachments. Although Exchange Server does not store content indexes in Exchange database files, the search catalog resides on the database drives.

The product development group completely revised the Microsoft Exchange Search Service. Content indexing is not only substantially faster than in earlier versions of Exchange Server, the size of the content index files is also substantially smaller. In Exchange Server 2007, the search catalog size drops from 30 percent to only 5 percent of the corresponding mailbox store database. Accordingly, Microsoft IT reserves five percent of the database drive for content indexing.

Unexpected Database Growth

Microsoft IT reserves at least 10 percent of space on the database drive for unexpected database growth. Mailbox databases can grow in size for several reasons, including mailbox moves, administrative maintenance, fragmentation, and so forth. The extra space also enables Microsoft IT to support up to 10 percent more users per server than defined in the mailbox server design, if necessary.

Transaction Logs

As mentioned earlier, the ESE writes all data to the transaction logs first to record all changes to the databases. As soon as the current log file is full, the storage engine renames the file and creates a new transaction log to write the next 1 MB of data. In Exchange Server 2007, transaction logs have a fixed size of 1 MB. Each storage group uses a separate set of transaction logs. However, smaller transaction log sizes and larger numbers of storage groups do not affect the storage requirements for the transaction logs. The amount of data that the ESE writes to the transaction logs depends on the transactions that the ESE must perform, but it does not depend on the storage group configuration or file size that it uses. A transaction log size of 1 MB instead of 5 MB only means that the ESE creates five times more log files that are five times smaller per storage group.

Using a large number of small transaction log files facilitates log shipping, which is the foundation of CCR. In any case, it is important to place the transaction logs on a set of dedicated physical drives so that the ESE can complete its write operations to the transaction logs efficiently and quickly.

Microsoft IT creates partitions that are four times smaller than the database drives to store the transaction log files that accumulate daily. This generous ratio ensures that Microsoft IT has sufficient free space on the transaction log drives to support migrating up to 1,500 users per day to Exchange Server 2007. For every byte of mailbox data moved to the target server, Exchange Server 2007 writes one byte of data to the transaction logs. Hence, a large number of transaction log files accumulate during mailbox migration. Between 20:00 and midnight, Microsoft IT runs full or incremental online backups that remove the transaction logs after the backup operation. In this way, Microsoft IT ensures that the transaction log drives do not run out of disk space between migration cycles.

Total Capacity Needs for Database and Transaction Log Drives

To determine the total capacity needs for the database drives, Microsoft IT uses the formula:

Number of Users * Mailbox Quota + 20% Database Overhead + 5% for Content Indexing + 10% Growth Reserve.

Table 5 lists the resulting storage requirements. Comparing these numbers with the information listed earlier in Table 3 reveals that Microsoft IT designed the storage solution for Exchange Server 2007 with ample space.

Table 5. Required Capacities for Database Drives

Server type

Number of users

Mailbox quota

User data

Database overhead

Content indexing

Growth reserve

Total

Mailbox

I

2,000

500 MB

1 Terabyte

200 GB

60 GB

120 GB

1.3 Tera-

bytes

Mailbox II

2,400

2 GB

4.5 Terabytes

960 GB

300 GB

600 GB

6.5 Tera-

bytes

Mailbox III

3,600

2 GB

7 Terabytes

1.4 Terabytes

450 GB

900 GB

9.75 Tera-

bytes

Table 6 refers to the total capacity needs for all transaction log drives combined in relation to the total size of the database drives according to a 25 percent size ratio. Again, a comparison with Table 3 reveals that Microsoft IT designed the mailbox servers with ample transaction log capacity.

Table 6. Required Capacities for Transaction Log Drives

Server type

Database drives (total)

Transaction log drives (total)

Mailbox I

1.3 Terabytes

350 GB

Mailbox II

6.5 Terabytes

1.6 Terabytes

Mailbox III

9.75 Terabytes

2.5 Terabytes

External Storage Configuration

Microsoft IT uses external storage enclosures to implement the storage solution for the Exchange Server 2007 mailbox servers. Servers in the Mailbox I and II categories use DAS. The original Mailbox III-type server design relied on a SAN-based solution. The different storage technologies reflect that Microsoft IT designed and deployed the Mailbox III server type during the Beta 1 timeframe. Important reliability features, such as CCR, were still in an early stage of development and did not achieve sufficient stability at that time. The SAN-based solution provided the necessary fault tolerance and redundancy for the Beta 1 mailbox servers. With the availability of Beta 2, however, Exchange Server 2007 proved to be the reliable release that Microsoft IT needed for a move to DAS in the storage design. All recent server deployments in the Mailbox I and Mailbox II categories use DAS-based storage.

In addition to migrating from SAN-based to DAS-based storage technology, Microsoft IT also intends to move from LFF to SFF disks in the Mailbox I design. The plan is to move approximately 66 percent of the deployment to the small form factor in the near future. Microsoft IT prefers SFF disks because of the lower power requirements, lower cost, and potentially higher reliability due to lower operating temperatures and better cooling in comparison to the large form factor. Furthermore, SFF storage enclosures occupy only one unit of rack space each. Saving rack space is a serious consideration for Microsoft IT in this large-scale deployment.

Universal Storage Building Blocks

To implement a flexible storage solution, Microsoft IT devised a modular design based on universal storage building blocks. A single building block consists of two storage enclosures and supports up to 1,200 users. The Mailbox I and II server types use two building blocks and the Mailbox III server types have three, according to the number of users in each design category. The Mailbox I server type uses 10 disks per storage enclosure, whereas the enclosures for the Mailbox II and III types contain 15 disks each. The disk capacity also varies. Mailbox I servers use 146 GB disks. The Mailbox II and Mailbox III designs rely on disks with a capacity of 300 GB.

Across the two storage enclosures (A and B), Microsoft IT mirrors the disks (A1-B1, A2-B2, A3-B3, and so forth) and then includes these mirrors in stripe sets to achieve a RAID 10 configuration. Per universal storage building block, Microsoft IT configures three hardware RAID 10 drives, as shown in Table 7.

Table 7. RAID 10 Configuration per Universal Storage Building Block

Server type

Capacity per disk

Disks per enclosure

RAID 10 drives

Comments

Mailbox I

146 GB

10

Drive 1: A1-A4
B1-B4
Drive 2: A5-A8 B5-B8
Drive 3: A9-A10 B9-B10

Drive 1 and drive 2 each have a raw capacity of 584 GB. This is sufficient to support 500 users per drive with a mailbox quota of 500 MB according to the following calculation:

500 * 500 MB = 250 GB + 50 GB [20% database overhead] = 300 GB + 15 GB [5% content indexing] = 315 GB + 32 GB (10% growth reserve) = 347 GB.

Drive 3 has a raw capacity of 292 GB. Microsoft IT creates two logical partitions on this drive. The raw capacity of each logical partition is 146 GB, exactly one fourth of the corresponding database drive capacity.

Mailbox II and Mailbox III

300 GB

15

Drive 1: A1-A6 B1-B6
Drive 2: A7-A12 B7-B12
Drive 3: A13-A15 B13-B15

Drive 1 and drive 2 each have a raw capacity of 1,650 GB. This is sufficient to support 600 users per drive with a mailbox quota of 2 GB according to the following calculation:

600 * 2 GB = 1,200 GB + 240 GB [20% database overhead] = 1,440 GB + 72 GB [5% content indexing] = 1,512 GB + 151 GB (10% growth reserve) = 1663 GB.

Drive 3 has a raw capacity of 825 GB. Microsoft IT creates two logical partitions on this physical drive. The raw capacity of each logical partition is 412 GB, exactly one fourth of the corresponding database drive capacity.

Universal Storage Building Blocks, Mailbox Databases, and Storage Groups

As outlined in Table 7, the largest universal storage building blocks support up to 600 users per database drive. With a quota of 2 GB per mailbox, this number signifies 1,440 GB of data in the Exchange Information Store. To keep the size of the mailbox databases files manageable, Microsoft IT distributes the data across seven mailbox databases per drive. Seven mailbox databases correspond to seven storage groups, which enables Microsoft IT to implement a consistent weekly backup schedule for each individual storage group, as explained later in this paper. Per server type, this implies that the mailbox databases remain below the following thresholds:

  • Mailbox I At a maximum number of 500 users per database drive and a quota of 500 MB, the mailbox database size remains below 50 GB under normal circumstances (500 / 7 = ~72 * 500 MB = 36 GB + 7.2 GB [20% database overhead] = 43.2 GB).
  • Mailbox II and III At a maximum number of 600 users per database drive and a quota of 2 GB, the mailbox database size remains below approximately 210 GB under normal circumstances (600 / 7 = ~86 * 2 GB = 172 GB + 34.4 GB [20% database overhead] = 206.4 GB).

According to CCR requirements, Microsoft IT places each mailbox database in separate storage group. This configuration also benefits transaction handling as mentioned in the section "Random Access Memory Configuration" earlier in this paper.

Fault Tolerance and Reliability

To achieve the desired level of fault tolerance and reliability in the DAS-based storage design, Microsoft IT connects the storage enclosures per universal storage building block to different controller ports (enclosure A connects to port 1 and enclosure B to port 2). Microsoft IT uses a dual-port SAS/Serial Advanced Technology Attachment (SATA) RAID controller. In this way, the storage building block can sustain a failure of an entire channel or enclosure.

Improved fault tolerance and reliability is also a reason why Microsoft IT configured RAID 10 drives for the transaction logs. Microsoft IT could have chosen a RAID 1 or RAID 5 configuration instead, but RAID 1 and RAID 5 can only tolerate a maximum of one disk failure. Furthermore, in the event of a disk failure, read performance drops by 50 percent and write performance is also measurably lower when rebuilding the disk array. In the Mailbox I design, the RAID 10 drive for the transaction logs uses four disks, whereas the Mailbox II and III design uses six disks. Correspondingly, this RAID configuration can tolerate a maximum of two (Mailbox I) or three (Mailbox II and III) disk failures and the I/O performance only drops by 25 percent (Mailbox I) or 16.6 percent (Mailbox II and III) in the event of a single disk failure.

In the Mailbox II and III design, the RAID 1 configuration might have untied the fifteenth disk in each storage enclosure. Disks A13 and B13 are necessary for the first RAID 1 drive and disks A14 and B14 for the second RAID 1 drive. Disks A15 and B15 could then serve as hot spares. However, Microsoft IT deemed the increased fault tolerance and capacity for the transaction log drive more important than the availability of a hot spare because Microsoft datacenters are staffed 24 hours, seven days per week. In the event of a disk failure, an IT specialist is readily available to replace the affected disk with minimum delay.

The RAID controllers that Microsoft IT currently uses support daisy-chained configurations with up to three enclosures per port. This implies that each RAID controller in the mailbox server design can support up to a maximum of three storage building blocks. To maintain fault tolerance, Microsoft IT connects the storage enclosures per universal storage building block to different ports, as mentioned in the previous section. Table 8 illustrates the resulting daisy-chain configuration per RAID controller port.

Table 8. Storage Enclosures per RAID Controller Port

Server Design

RAID Controller Port 1

RAID Controller Port 2

Comments

Mailbox I and II

A, C

B, D

The Mailbox I and II designs use two USBBs with the enclosure pairs A-B and C-D.

Mailbox III

A, C, E

B, D, F

The Mailbox III design uses three USBBs with the enclosure pairs A-B, C-D, and E-F.

RAID Controller Configuration

To implement the storage solution, Microsoft IT decided to use DAS-based RAID controllers with a 256 MB battery-backed cache and SAN-based controllers with a battery-backed cache of 16 GB. Microsoft IT leaves the write cache on all controllers enabled to achieve a good Exchange Server performance. Disabling the write cache degrades the controller performance by more than 30 percent. It is a general recommendation to use the write cache on computers running any version of Exchange Server.

Logical Storage Configuration

Microsoft IT mailbox servers own a large number of logical drives, Including:

  • System drive Microsoft IT places operating system and page file on the system drive.
  • Drives for binary files and tools The Exchange Server 2007 binary files and message tracking logs reside on a separate logical drive.
  • Databases and transaction log drives The number of database and transaction log drives depends on the number of USBBs. Mailbox servers in the Mailbox I and II category have four database and four transaction log drives. Mailbox III-type servers have two additional database and transaction log drives.
  • Backup drives Microsoft IT uses a separate RAID controller with a separate set of disks to implement disk-based backup storage. These drives only exist on the active nodes in CCR clusters, as explained later in this document.

Microsoft IT uses a similar logical drive configuration on all mailbox servers, with the exception that the number of logical drives varies between the mailbox server categories. Among other things, the drive letter consistency enables Microsoft IT to use almost identical Windows PowerShell scripts to configure all mailbox servers. If the number of drives exceeds the range of possible drive letters on a mailbox server, Microsoft IT uses volume mount points (NTFS file system junction points).

Exchange Server Backup Solution

Like most IT organizations, Microsoft IT relies on backup strategies to help protect the company against loss or damage of business data and to meet regulatory retention requirements. Concerning data protection, however, backup technology has limitations. Although the ideal solution protects without latency and facilitates instant recovery, backup technology confines the possibilities to achieve this ideal.

For example, Microsoft IT performed daily full backups between 20:00 and midnight on all Exchange 2003 mailbox servers. Each backup cycle included approximately 1.2 Terabytes of messaging data. This meant that the Exchange 2003 backup required a substantial amount of time and the restore of a corrupted database was not instantaneous. Fully restoring 1.5 Terabytes of data likely takes more than a business day. Microsoft IT mitigated the issue by using server clusters, fault-tolerant RAID volumes in a SAN, and by keeping individual databases below 50 GB in size, which helped to reduce restore times for individual databases. However, it takes new technologies to eliminate old barriers. With Exchange Server 2007, Microsoft IT can use CCR to perform backups continuously based on transaction log shipping to a passive node in a server cluster.

The backup strategy that the Microsoft IT Exchange messaging team devised for Exchange Server 2007 relies on the three redundancy levels: mailbox store, transport dumpster on Hub servers, and database backups. If redundancy at the mailbox store level fails, Microsoft IT can recover the messages from the transport dumpster, and if the transport dumpster redundancy fails, Microsoft IT still has the option to recover the data using an online backup as a last resort.

Mailbox Store

Microsoft IT configures all Exchange Server 2007 mailbox servers in CCR clusters. The CCR configuration that Microsoft IT decided to implement relies on two-node Majority Node Set (MNS) server clusters with file share witness. Unlike a traditional Exchange Server cluster with shared quorum on shared disks (SAN-based storage solution), MNS clusters use separate storage subsystems. Each cluster node stores a copy of the MNS quorum on the local system drive and keeps it synchronized with the other nodes. The Microsoft Exchange Replication Service synchronizes the mailbox store databases across both nodes on a continuous basis by using log shipping. The mailbox server with all the data is readily available on the passive node if the active node fails.

Because there is no need to configure a shared storage subsystem, CCR server clusters simplify the mailbox server deployment. All cluster nodes can use DAS. Although equipping all nodes with the same hardware is not necessary, Microsoft IT uses identical hardware configurations so that failover to the passive node can occur without performance penalties.

In any case, the logical drive letters for the system drive, the drives for the binary files of Exchange Server and the message tracking log files, and the drives for the database and the transaction logs must be identical on all nodes. After a failover, the EVS expects to find all files at the same locations. Furthermore, it is important to note that CCR requires a single mailbox store database per storage group (50 storage groups maximum).

Microsoft IT also uses identical network interface cards (NICs) in the active and passive nodes. Each node has two Gigabit Ethernet NICs on board, which Microsoft IT uses to connect the nodes to the public network of the cluster. A third Gigabit Ethernet NIC, Microsoft IT installs in each node to establish the private network connection. The nodes use the private network for cluster communication, such as for cluster heartbeats. The public network cards support both client and cluster communications to provide redundancy if the private network fails.

Transport Dumpster

Microsoft IT configures the Hub Transport servers to retain a copy of all messages delivered to clustered mailbox servers. The messages remain for a specified period in a special message queue, called the transport dumpster queue, and are available during that time for redelivery. For example, a clustered mailbox server (CCR configuration) in the local Active Directory site may request redelivery after a failover with data loss to receive the most recent messages that the Microsoft Exchange Replication Service on the passive node may not have had a chance to replicate from the previously active node.

It is important to enable the transport dumpster feature on all Hub Transport servers in Active Directory sites that contain CCR server clusters, so that clustered mailbox servers can request redelivery. Redelivery can be necessary if a failover occurs to a passive node before CCR has copied the most recent messages. The transport dumpster is disabled by default. By using the set-TransportConfig PowerShell command, Microsoft IT enables this feature on all Hub Transport servers with the following parameters:

  • MaxDumpsterSizePerStorageGroup This parameter specifies the maximum size of the transport dumpster queue for each storage group. According to product recommendations, the size should be 1.25 times the size of the largest message. At Microsoft, the largest messages are 10 MB in size, so Microsoft IT specifies 15 MB for this parameter.
  • MaxDumpsterTime This parameter specifies for how long the Hub Transport server can retain messages in the transport dumpster queue. Microsoft uses a value of 07.00:00:00, which corresponds to seven days.

Additional disk space is necessary to accommodate the transport dumpster queue on each Hub Transport server. For example, in the largest Microsoft data center in the Northwest of the United States, Microsoft IT hosts mailbox servers with approximately 1,000 storage groups. With a transport dumpster queue size of 15 MB per storage group, the additional disk space on the Hub Transport servers required for this feature is approximately 15 GB (1,000 × 15 MB = ~15 GB).

Online Database Backups

Microsoft IT performs online database backups on a daily basis as an additional measure of protection. For example, if an active node in a Microsoft IT two-node MNS cluster fails, only one node remains with the data. There is a lack of redundancy until Microsoft IT repairs and reseeds the databases on the affected node.

The database backups close the gap. However, the redundancies already implemented at the message transport and mailbox store levels (CCR) enable Microsoft IT to reduce the amount of data per backup cycle in comparison to Exchange Server 2003. Instead of running a full backup every day, Microsoft IT now performs full backups only once per week and performs incremental backups daily.

The increased redundancy for the Exchange Information Store and the fact that Microsoft IT is not required to keep data on tape enables Microsoft IT to eliminate tape backups and lower operational costs. To accomplish this goal, the Exchange messaging team has developed the following online backup strategy for the Exchange Server 2007 mailbox servers in the production environment.

Disk-Based Backup Storage

Microsoft IT uses a separate RAID controller with a separate set of 500 GB SATA or low-cost fibre channel disks in a RAID 5 configuration on each active node in the CCR clusters to implement disk-based backup storage. The passive nodes do not have this extra storage because Microsoft IT does not perform online backup operations on replica nodes.

The current Microsoft IT backup solution supports only streaming backups and does not support backup operations on passive database copies. A new backup solution based on Microsoft Data Protection Manager V2.0 (DPMv2) and Volume Shadow Copy Service (VSS) is currently under development to support backup operations in much more frequent intervals on passive nodes than is possible with streaming online backups on active nodes. The new backup solution is entirely software-based and does not rely on VSS hardware providers.

Online Backup Procedure

Until the VSS-based DPMv2 backup solution is available, Microsoft IT continues to use streaming disk-to-disk backup procedures controlled through command-line scripts to perform online backups through the Windows Backup program (NTBackup.exe). The streaming technology supports backing up mailbox databases in different storage groups in parallel. This is the main reason why Microsoft IT configured seven storage groups per database drive in a universal storage building block. Using seven storage groups, Microsoft IT can stagger the full and incremental online backups of the storage groups on the database drive across a seven-day week period, as shown in Table 9.

Table 9. Legacy Streaming Backup Schedule per Database Drive

Storage group

Mon

Tue

Wed

Thu

Fir

Sat

Sun

SG 1

Full

Inc

Inc

Inc

Inc

Inc

Inc

SG 2

Inc

Full

Inc

Inc

Inc

Inc

Inc

SG 3

Inc

Inc

Full

Inc

Inc

Inc

Inc

SG 4

Inc

Inc

Inc

Full

Inc

Inc

Inc

SG 5

Inc

Inc

Inc

Inc

Full

Inc

Inc

SG 6

Inc

Inc

Inc

Inc

Inc

Full

Inc

SG 7

Inc

Inc

Inc

Inc

Inc

Inc

Full

The backup storage provides sufficient capacity to store two full backups and 12 incremental backups of the mailbox server's messaging databases on the backup drives. With a full online backup every seven days and incremental backups during the remaining six days, Microsoft IT can store the backups of the last eight to 14 days on the disks. The Windows Backup performance of 20 MB per second per backup stream enables Microsoft IT to schedule online maintenance cycles for the messaging databases according to the default configuration of Exchange Server 2007.

Conclusion

When Microsoft IT finishes the migration of 130,000 users to Exchange Server 2007 at the end of 2006, Microsoft IT will have deployed 124 cluster nodes for 62 mailbox servers that host almost 2,000 storage groups and corresponding mailbox store databases worldwide.

The investment in time and materials is justified because Microsoft IT will realize tangible and intangible business benefits with Exchange Server 2007. The tangible benefits enable Microsoft IT to lower total cost of ownership (TCO) without adverse impact on existing business processes. Intangible benefits, on the other hand, strengthen the productivity and agility of employees, partners, and other business associates.

Tangible benefits that Microsoft IT realizes with the migration to Exchange Server 2007 include:

  • Lower storage costs By replacing SAN-based storage solutions with DAS-based storage solutions, Microsoft IT saves storage costs while at the same time increasing mailbox sizes by up to a factor of 10.
  • Eliminate tape backups By replacing backups to tape with a solution based on backups to disk, Microsoft IT saves $5 million per year in backup tape costs alone while at the same time building the foundation for better backup service level agreements (SLAs) in comparison to previous versions of Exchange Server.

Intangible benefits that Microsoft IT realizes with the migration to Exchange Server 2007 include:

  • Increased employee productivity By providing sufficient Exchange Server storage for users to keep all their messages on the mailbox server, Microsoft IT can provide users with centralized access to all their messages and other items, such as voice mail. Microsoft IT can include all user data in daily and continuous backups to prevent loss of business-critical information. Moreover, new features, such as Unified Messaging, will have a positive impact on user productivity because all information is available in a single location—the mailbox.
  • Compliance with legal and regulatory requirements By disabling personal folder stores on user computers and increasing mailbox sizes up to 2 GB, Microsoft IT can provide a centralized and easily searchable message store and centrally enforce message policies without negative impact on employee productivity.
  • Improved messaging protection By deploying Edge Transport servers to handle all incoming and outgoing Internet mail messages, Microsoft IT can block unwanted messages (such as spam) and viruses before they reach the production environment. At the same time, Microsoft IT can decrease the number of false positives through scheduled Sender Reputation Level (SRL) and Spam Confidence Level (SCL) definition file updates.
  • Establishment of foundation for new SLAs By deploying high-availability features, such as transport dumpster and CCR, on two-node server clusters without shared storage, Microsoft IT can implement new backup procedures to support the emerging requirements in the production environment.
  • Simplified operational tasks By using the new scripting capabilities based on Windows PowerShell, Microsoft IT can automate server deployments and administrative tasks, and lower operational overhead.
  • Demonstrated confidence in the product By migrating the entire production environment with 130,000 users to Exchange Server 2007, starting at Beta 1 and completing at RTM, Microsoft IT demonstrated the confidence of Microsoft in the new Exchange Server version to customers while at the same time helping developers to ship an optimized product that has proven itself in a large-scale enterprise environment.

For More Information

For more information about Microsoft products or services, call the Microsoft Sales Information Center at (800) 426-9400. In Canada, call the Microsoft Canada information Centre at (800) 563-9048. Outside the 50 United States and Canada, please contact your local Microsoft subsidiary. To access information through the World Wide Web, go to:

http://www.microsoft.com

http://www.microsoft.com/technet/itshowcase

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