Exchange Server 5.5 secrets® Connect Individuals, Workgroups, and Companies With its additional Internet protocol support and existing e-mail and groupware standards, Exchange Server 5.5 brings a unique communication and collaboration solution to businesses of all sizes. Take full command of Exchange Server's new features and proven capabilities with the combined expertise of four veteran Exchange consultants and instructors. In this insightful guide, Robert Guaraldi, Jennifer Sides, Ned Studt, and Jerry Condon bring you the insider knowledge and field experience needed to build a solid e-mail, groupware, and workflow platform. Your Insider Guide to Exchange Server 4.0 – 5.5 Administration
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About the Authors Robert Guaraldi, president of Valinor and prolific author, is one of the very few people in the world outside of Microsoft authorized to teach the Microsoft Exchange ten-day PSS class. Jennifer Sides, an executive at IKON, is also authorized to teach the Microsoft Exchange ten-day PSS class. Ned Studt, a senior engineer and chief messaging architect at IKON, has been hailed by Microsoft as one of the top messaging consultants in the US. Jerry Condon, manager of technical documentation and course-ware development at IKON, has managed and coauthored numerous white papers and documentation projects.Excerpt. © Reprinted by permission. All rights reserved.:
Single Site, Multiple Servers
Excerpted from Chapter 27 of Exchange Server 5.5 Secrets®
by Robert Guaraldi, Jennifer Sides, Ned Studt,
and Jerry Condon
Featuring:Intrasite communications Private Information Store System Attendant The definitive statement is that the only justification to maintain a single server in an Exchange site would be that of cost. A second Exchange server within a site provides redundancy and adds flexibility to your site. The argument that multiple servers add a great deal of administrative overhead just isn't true, because most administration is performed at the site level.
However, we should also add that having two or more servers in an Exchange site does add a level of complexity. For example, by adding the second server, you have added issues like intrasite communications, intrasite directory communications and replication. Fortunately, none of that is of concern to the administrator because the Exchange server handles all of this without administrative intervention or interaction. Let's drill down on this topic.
Within an Exchange site there is a lot of different information that passes between servers and components. Between servers within a site, however, there are only two components that are capable of actually establishing intraserver communications. These are the MTA and the directory.
All non-directory information that passes between servers in a site passes through the MTA. This is not to say that the directory and MTA are the only components capable of message generation but that the MTA serves as the sole mechanism for transferring this information.
Through directory information, all MTAs are completely aware of all other Exchange servers within a site. Intrasite communication is always one hop in nature, meaning that any server within a site can directly communicate with any other server in a site. This communication is shown in Figure 27-1.
Figure 27-1: Intrasite communications.
Directory service communication and replication
The directory service (DS) is responsible for storing and organizing information about the Exchange organization and user account information. All servers in a site are cognizant of this information through a process called replication.
Directory replication within a site is performed in a multi-master fashion, with every server holding a complete copy of the directory after accounting for usually minor latency.
The replication is performed by direct communication between the directories, as shown in figure 27-2. When a change is made, the directory will delay the replication of that information for 5 minutes.
Figure 27-2: Directory Communication.
Instead of pushing changes to each other server in a site, the directory simply sends a notification of changes to each server, which is then responsible for retrieving those changes from the server that owns them.
While all of this takes place in the background, this type of replication provides one very important benefit: redundancy. A server that goes down in a multi-server site doesn't have the impact you get in a single server site since each server has a complete copy of the directory. It takes much less time to restore a server in a multi-server site than in a single server site.
Note: The NT registry key: HKEY_LOCAL_MACHINE\System\
Replicator notify pause after modify controls the latency of delivering modifications after changes are made.
Private information store
When the information store receives messages destined for a user on another server in the site, it notifies the MTA, which handles the transfer of the message to the other server.
Public Information store
The public information store handles all information in the public store. Information the public store may send is the structure and replicas. We will cover these items in more detail later.
The system attendant creates and tracks messages related to link and server monitors. The link monitor verifies the message path to a particular server by sending an IPM (a message). The server monitor similarly uses messages to communicate with another SA on the other server. The system attendant is the component responsible for generating this traffic, but it passes through the MTA.
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