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These decisions cannot be made effectively without an understanding of how
the Directory Server handles these concepts. For example, when you decide
what information you want to replicate, you need to know what is the smallest
replication unit that the Directory Server can handle. The following sections
contain definitions of concepts used by the Directory Server. This provides a
framework for thinking about the global decisions you need to make.
Unit of Replication
In Directory Server (6.x), the smallest unit of replication is a database. This
means that you can replicate an entire database, but not a subtree within a
database. Therefore, when you create your directory tree, you must take your
replication plans into consideration. For more information on how to set up
your directory tree, refer to Chapter 5, "Designing the Directory Topology."
The replication mechanism also requires that one database correspond to one
suffix. This means that you cannot replicate a suffix (or namespace) that is
distributed over two or more databases.
Read-Write Replica/Read-Only Replica
A database that participates in replication is defined as a replica. There are two
kinds of replicas: read-write or read-only. The read-write replicas contain master
copies of directory information and can be updated. Read-only replicas refer all
update operations to read-write replicas.
Supplier/Consumer
A server that holds a replica that is copied to a replica on a different server is called
a supplier for that replica. A server that holds a replica that is copied from a
different server is called a consumer for that replica. Generally, the replica on the
supplier server is a read-write replica, and the one on the consumer server is a
read-only replica. There are exceptions to this statement:
•
In the case of cascading replication, the hub supplier holds a read-only replica
that it supplies to consumers. For more information, refer to "Cascading
Replication," on page 117.
•
In the case of multi-master replication, the masters are suppliers and
consumers for the same read-write replica. For more information, refer to
"Multi-Master Replication," on page 113.
In Directory Server (6.x), replication is always initiated by the supplier server,
never by the consumer, in contrast to earlier versions of the Directory Server
that allowed consumer-initiated replication (where you configure consumer
servers to pull data from a supplier server).
Chapter 6
Designing the Replication Process
Introduction to Replication
109
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