Designing The Directory Topology; Topology Overview; Distributing The Directory Data - Red Hat DIRECTORY SERVER 8.1 - DEPLOYMENT Deployment Manual

Chapter 5.

Designing the Directory Topology

Chapter 4, Designing the Directory Tree
covers how to design the directory service stores entries.
Because Red Hat Directory Server can store a large number of entries, it is possible to distribute
directory entries across more than one server. The directory's topology describes how the directory
tree is divided among multiple physical Directory Servers and how these servers link with one another.
This chapter describes planning the topology of the directory service.

5.1. Topology Overview

Directory Server can support a distributed directory, where the directory tree (designed in Chapter 4,
Designing the Directory Tree) is spread across multiple physical Directory Servers. The way the
directory is divided across those servers helps accomplish the following:
• Achieve the best possible performance for directory-enabled applications.
• Increase the availability of the directory service.
• Improve the management of the directory service.
The database is the basic unit for jobs such as replication, performing backups, and restoring data. A
single directory can be divided into manageable pieces and assigned to separate databases. These
databases can then be distributed between a number of servers, reducing the workload for each
server. More than one database can be located on a single server. For example, one server might
contain three different databases.
When the directory tree is divided across several databases, each database contains a portion of
the directory tree, called a suffix. For example, one database can be used to store only entries in the
ou=people, dc=example,dc=com suffix, or branch, of the directory tree.
When the directory is divided between several servers, each server is responsible for only a part of the
directory tree. The distributed directory service works similarly to the Domain Name Service (DNS),
which assigns each portion of the DNS namespace to a particular DNS server. Likewise, the directory
namespace can be distributed across servers while maintaining a directory service that, from a client's
point of view, appears to be a single directory tree.
The Directory Server also provides knowledge references, mechanisms for linking directory data
stored in different databases. Directory Server includes two types of knowledge references; referrals
and chaining.
The remainder of this chapter describes databases and knowledge references, explains the
differences between the two types of knowledge references, and describes how to design indexes to
improve the performance of the databases.

5.2. Distributing the Directory Data

Distributing the data allows the directory service to be scaled across multiple servers without
physically containing those directory entries on each server in the enterprise. A distributed directory
can therefore hold a much larger number of entries than would be possible with a single server.
In addition, the directory service can be configured to hide the distribution details from the user. As far
as users and applications are concerned, there is only a single directory that answers their directory
queries.
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