Properly Sizing Exchange Server 2003

Before delving into recommended configurations for Exchange Server 2003, it is essential to not only understand the fundamentals of this messaging system but also the dependencies and interactions those components have with the underlying operating system (that is, Windows Server 2003). Being a client-server messaging application, maximizing Exchange Server 2003 involves fine-tuning all of its core and extended components. Optimization of each of these components affects the overall performance of Exchange.

The core components of Exchange Server (for example, the information stores, connectors, transaction logs, and more) have a direct bearing on gauging resource requirements. The number of users in a messaging environment and the various Exchange functions are equally influential.

Optimizing the Disk Subsystem Configuration

There are many factors—such as the type of file system to use, physical disk configuration, database size, and log file placement—that need to be considered when you are trying to optimize the disk subsystem configuration.

Choosing the File System

Among the file systems supported by Windows Server 2003 (that is, FAT and NTFS), it is recommended to use only NTFS on all servers—especially those in production environments. NTFS provides the best security, scalability, and performance features. For instance, NTFS supports file and directory-level security, large file sizes (files of up to 16TB), large disk sizes (disk volumes of up to 16TB), fault tolerance, disk compression, error detection, and encryption.

Choosing the Physical Disk Configuration

Windows Server 2003, like its predecessors, supports RAID (Redundant Array of Inexpensive Disks). The levels of RAID supported by the operating system are

• RAID 0 (Striping)

• RAID 1 (Mirroring)

• RAID 5 (Striping with Parity)

There are various other levels of RAID that can be supported through the use of hardware-based RAID controllers.

The deployment of the correct RAID level is of utmost importance because each RAID level has a direct effect on the performance of the server. From the viewpoint of pure performance, RAID level 0 by far gives the best performance. However, fault tolerance and the reliability of system access are other factors that contribute to overall performance. The skillful administrator strikes a balance between performance and fault tolerance without sacrificing one for the other. The following sections provide recommended disk configurations for Exchange Server 2003.

Disk Mirroring (RAID 1)

In this type of configuration, data is mirrored from one disk to the other participating disk in the mirror set. Data is simultaneously written to the two required disks, which means read operations are significantly faster than systems with no RAID configuration or with a greater degree of fault tolerance. Write performance is slower, though, because data is being written twice—once to each disk in the mirror set.

Besides adequate performance, RAID 1 also provides a good degree of fault tolerance. For instance, if one drive fails, the RAID controller can automatically detect the failure and run solely on the remaining disk with minimal interruption.

The biggest drawback to RAID 1 is the amount of storage capacity that is lost. RAID 1 uses 50% of the total drive capacity for the two drives.

Disk Striping with Parity (RAID 5)

In a RAID 5 configuration, data and parity information is striped across all participating disks in the array. RAID 5 requires a minimum of three disks. Even if one of the drives fails within the array, the Exchange Server 2003 server can still remain operational.

After the drive fails, Windows Server 2003 continues to operate because of the data contained on the other drives. The parity information gives details of the data that is missing due to the failure. Either Windows Server 2003 or the hardware RAID controller also begins the rebuilding process from the parity information to a spare or new drive.

RAID 5 is most commonly used for the data drive because it is a great compromise among performance, storage capacity, and redundancy. The overall space used to store the striped parity information is equal to the capacity of one drive. For example, a RAID 5 volume with three 200GB disks can store up to 400GB of data.

Hardware Versus Software RAID

Hardware RAID (configured at the disk controller level) is recommended over software RAID (configurable from within the Windows Server 2003) because of faster performance, greater support of different RAID levels, and capability of recovering from hardware failures more easily.

Database Sizing and Optimization

As mentioned throughout this book, Exchange Server 2003 is available in two versions: Standard and Enterprise. The Standard Edition supports one storage group with one private and one public information store. The maximum information store (database) size is 16GB. The Enterprise Edition provides support for up to four storage groups with a combined total of 20 useable databases per server with practically unlimited database size.

The flexibility with the Enterprise Edition is beneficial not just in terms of growth but also performance and manageability. More specifically, the advantages for segmenting can include the following:

• Administrators are enabled to segment the user population on a single Exchange server.

• Multiple mailboxes can more evenly distribute the size of the messaging data and help prevent one database from becoming too large and possibly unwieldy for a given system.

• Multiple databases present greater opportunities for faster enumeration of database indexing.

• Multiple databases can be segmented onto different RAID volumes and RAID controller channels.

• Transaction logs can be segmented from other log files using separate RAID volumes.

• Failures such as database corruption affect a smaller percentage of the user population.

• Offline maintenance routines require less scheduled downtime, and fewer users are affected.

Determining the number of storage groups and databases for Exchange Server 2003 should also be based on workload characterization. Users can be grouped based on the how they interact with the messaging system (for example, in terms of frequency, storage requirements, and more). Users placing higher demands on Exchange Server 2003 can be placed into a separate storage group and separate databases so that the greater number of read/write operations do not occur in the same database and are more evenly distributed.

Optimizing Exchange Logs

Similar to the previous versions of Exchange, transaction log files should be stored on separate RAID volumes. This enables significant improvements in disk input/output (I/O) operations. Transaction logs are created on a per storage group level rather than per database. Therefore, when you have multiple storage groups, multiple log files are created that enable simultaneous read and write operations. If the transaction logs are then placed on separate RAID volumes, there can be significant improvements to performance.

Sizing Memory Requirements

The recommended starting point for the amount of memory an Exchange Server 2003 server is installed with is 256MB. The specific memory requirements naturally vary based on server roles, server responsibilities, and the number of users to support. In addition, some organizations define certain guidelines that must be followed for base memory configurations. A more accurate representation of how much memory is required can be achieved by baselining memory performance information gathered from the Performance snap-in or third-party tools during a prototype or lab testing phase.

Another important factor to take into consideration is when the organization adds functionality to Exchange Server 2003 or consolidates users onto fewer servers. This obviously increases resource requirements, especially in terms of adding more physical memory. In these scenarios, it is recommended to use the base amount of memory (for example, 256MB) and then add the appropriate amount of memory based on vendor specifications. It is also important to consult with the vendor to determine what the memory requirements may be on a per user basis. This way the organization can plan ahead and configure the proper amount of memory prior to needing to scale to support a larger number of users in the future.

Sizing Based on Server Roles

Server roles can have a considerable bearing on both the performance and capacity of Exchange Server 2003. Based on the various roles of the Exchange servers, the strategic placement of Exchange services and functionality can greatly improve performance of the overall messaging system while reducing the need for using additional resources. By the same token, a misplaced Exchange service or functional component can noticeably add to network traffic and degrade the overall performance of the messaging system.

Servers are generally divided into two sets of roles: front-end and back-end servers. Within these two sets of roles are several key roles that an Exchange Server 2003 server can serve, including, but not limited to, OWA, public folder, mailbox store, or bridgehead server.

Front-end servers are the first point of contact for client messaging requests. The servers proxy these requests to the back-end servers for processing. The front-end/back-end topology is recommended for organizations that use OWA, POP, or IMAP for employees accessing the messaging system over the Internet.

Another key difference between a front-end and back-end server is storage requirements. Back-end servers usually host mailbox or public folder stores, and front-ends have minimal requirements. Back-end servers, therefore, usually have much higher and greater storage requirements, as well as processing power and memory requirements.

Front-end Server Sizing

There are various factors that affect the performance of a front-end server, including the following:

• The number and type of protocols supported

• The number of users supported

• The authentication methods supported

• Encryption requirements

Tables 33.1 through 33.3 show the recommended resource requirements of various dedicated front-end servers. It is important to note that these guidelines are minimum recommendations, and actual requirements may vary depending upon the organization.

Table 33.1. Recommended Minimum POP3 Front-end Server Configurations

Resource	Description
RAM	256MB.
Processor	Pentium III 800MHz or higher processor.
Hard disk	RAID 1 for Windows Server 2003 and Exchange Server 2003 (assuming no mail is stored on the front-end server and logging is not enabled).
Network	100Mbps or higher NIC(s).
Other considerations	If connections to this server are over SSL consider using a NIC that offloads SSL processing.

Table 33.2. Recommended Minimum OWA or IMAP4 Front-end Server Configurations

Resource	Description
RAM	256MB plus 512KB of RAM per active, concurrent client connection.
Processor	Dual Pentium III 800MHz or higher processors.
Hard disk	RAID 1 for Windows Server 2003 and Exchange Server 2003 (assuming no mail is stored on the front-end server and logging is not enabled).
Network	100Mbps or higher NIC(s).
Other considerations	If connections to this server are over SSL consider using a NIC that offloads SSL processing.

Table 33.3. Recommended Minimum SMTP Front-end Server Configurations

Resource	Description
RAM	Recommended 512MB to manage large queues.
Processor	Dual Pentium III 800MHz or higher processors.
Hard disk	RAID 1 can be used for Windows Server 2003 and Exchange Server 2003. If large amounts of disk space are required for SMTP queues, a separate RAID 0+1 volume can be used.
Network	100Mbps or higher NIC(s).
Other considerations	Encrypting the SMTP traffic using TLS (Transport Layer Security) does not necessarily require significantly more memory or processing power.

Back-end Server Sizing

As mentioned earlier, back-end servers generally host mailbox and public folder stores. They can also provide various other functions, including features that are typically thought of as front-end functions.

The myriad of functionality options and other considerations (for example, the number of users to support, mailbox store size(s), incoming and outgoing message size restrictions, security requirements, and more) can make back-end server sizing a daunting task at best. As a best practice, it is recommended that an Exchange Server 2003 server be configured with a minimum of 512MB of memory and dual processors. Physical memory has been, and continues to be, an inexpensive component and is one of the easiest ways to upgrade a server. As such you might even consider using 1GB as a minimum standard for back-end servers. For the disk subsystem, it is recommended to implement three hardware-based RAID volumes: a RAID 1 volume for Windows Server 2003 and Exchange Server 2003 system-related files, a RAID 5 volume for the mailbox and public folder stores, and another RAID 1 volume for transaction logs. The number of volumes for the transaction logs may vary depending on the number of storage groups configured on the server.