Unit Of Replication - Red Hat DIRECTORY SERVER 8.1 - DEPLOYMENT Deployment Manual

Chapter 6. Designing the Replication Process
These decisions cannot be made effectively without an understanding of how the Directory Server
handles these concepts. For example, decide what information to replicate, be aware of the smallest
replication unit that the Directory Server can handle. The replication concepts used by the Directory
Server provide a framework for thinking about the global decisions that need to be made.

6.1.1.1. Unit of Replication

The smallest unit of replication is a database. An entire database can be replicated but not a subtree
within a database. Therefore, when defining the directory tree, always consider replication. For more
information on how to set up the directory tree, see
The replication mechanism also requires that one database correspond to one suffix. A suffix (or
namespace) that is distributed over two or more databases cannot be replicated.
6.1.1.2. Read-Write and Read-Only Replicas
A database that participates in replication is defined as a replica. Directory Server supports two
types of replicas: read-write and 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.
6.1.1.3. Suppliers and Consumers
A server that stores a replica that is copied to a different server is called a supplier. A server that
stores a replica that is copied from a different server is called a consumer. Generally speaking, the
replica on the supplier server is a read-write replica; the replica on the consumer server is a read-only
replica. However, the following exceptions apply:
• In the case of cascading replication, the hub supplier holds a read-only replica that it supplies to
consumers. For more information, see
• In the case of multi-master replication, the suppliers function as both suppliers and consumers for
the same read-write replica. For more information, see
NOTE
In the current version of Red Hat Directory Server, replication is always initiated by the
supplier server, never by the consumer. This is unlike earlier versions of Directory Server,
which allowed consumer-initiated replication (where consumer servers could retrieve data
from a supplier server).
Suppliers
For any particular replica, the supplier server must:
• Respond to read requests and update requests from directory clients.
• Maintain state information and a changelog for the replica.
• Initiate replication to consumer servers.
The supplier server is always responsible for recording the changes made to the read-write replicas
that it manages, so the supplier server makes sure that any changes are replicated to consumer
servers.
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Chapter 4, Designing the Directory
Section 6.2.3, "Cascading
Section 6.2.2, "Multi-Master
Tree.
Replication".
Replication".