Datasheet

22 Chapter 1
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Preparing for the Exchange Installation
If a site has multiple domain controllers, consider using a Bridgehead server for
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Active Directory replication to other sites.
Install the right number of Global Catalog servers in each site to support the applica-
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tions. When using 32-bit domain controllers, the ratio of Global Catalog processor
cores to Exchange Mailbox server processor cores is 1 to 4. When using 64-bit Global
Catalogs with enough memory to cache the entire Active Directory, the ratio is 1 to 8.
Summary
The better you understand how the Exchange system works, the better you’ll be able to
plan a viable network and troubleshoot that network when problems occur. This chapter
examined three basic aspects of Exchange Server architecture: how Exchange is integrated
with Active Directory, how information is stored and organized in Active Directory, and
how messages flow within an Exchange organization.
At the top of the Active Directory hierarchy is the domain forest, which represents the
outside boundary that any Exchange organization can reach. A domain tree is a hierar-
chical arrangement of domains that share a common namespace. The first domain in a
tree is the root domain. Domains added under this are child domains. Within the domain
tree, domains establish trust relationships with one another that allow objects in a trusted
domain to access resources in a trusting domain. A domain is a group of computers and
other resources that are part of a network and share a common directory database. Each
domain contains at least one domain controller. Multiple domain controllers per domain
can be used for load balancing and fault tolerance.
When Exchange is installed, many objects, such as users, are enhanced with Exchange-
related features. A global catalog holds information about all the objects in a forest.
Objects can be grouped into organizational units that allow administrators to manage large
groups of similar objects effectively at the same time.
Within Active Directory, five partitions store certain pieces of the total information that
makes up Active Directory. These partitions are the domain partition, configuration parti-
tion, schema partition, global catalog partition, and application partition(s). There can be
multiple application partitions within the forest and domains.
Although Active Directory uses multimaster replication, there are five specific roles that
only one domain controller in a forest or domain can hold at any one time. The five roles are
the domain naming master (one per forest), schema master (one per forest), infrastructure
master (one per domain), PDC emulator master (one per domain) and RID master (one per
domain). The failure of a domain controller holding each role will have different effects on
the forest and domain. Exchange Server 2007 must contact the domain controller holding
the schema master role during setup to modify and extend the schema.
Active Directory is loosely consistent, meaning that not every domain controller in the
forest with a certain partition will have the same information at any time. However, over