With the help of replication, copies of identical data can be made available across multiple servers. OUD 11g provides numerous advanced replication capabilities. Lets see the different concepts/term used.
1) OUD uses multimaster replication.
a) Multiple master directory server replicas can coexist in a
directory services topology.
b) Changes made to any master directory server are automatically
propagated to other master directory servers in the topology.
c) All the directory servers in a replication topology can accept read and write operations. We can configure servers in a replication topology as read-only replicas if desired.
2) Fractional Replication
a) In this, we can define a set of attributes—for example, social security numbers or PIN codes—that are not replicated to less secure parts of your directory services topology.
b) Helps achieve compliance with various regulations and security mandates.
c) Also assists in optimizing replication over a wide-area network by enabling you to replicate only the most critical attributes in your directories.
3) Assured Replication
a) Changes are confirmed to the client application only after information
has been safely propagated to multiple directory instances.
b) Uses tighter consistency model which means control is returned to the client after the changes to attributes have been replicated to the other directory server.
4) Loose Consistency Replication Model
a) OUD replication is loosely consistent by default.
b) Changes made on one directory server are replayed asynchronously to the other servers in the topology. This basically means that same entries can be modified simultaneously on different servers. As a result, conflicts can occur and they need to be resolved, either automatically with the help of conflict rules or manually.
5) Isolated Replication
a) An isolated replica is a directory server that can accept changes from other replicas but cannot send changes to the replication server to which it is connected.
b) Cannot be the source of data updates to the topology.
5) OUD replication requires 2 kind of servers: Directory Server which can store directory data and process LDAP operations from clients. & Replication Server which propagate updates among a set of directory servers configured as replicas.
6) Replication servers can run in their own separate processes or they can run as separate threads in the same process as directory servers.