Adding a Replica

Add a replica to a server to provide your directory with

• Fault tolerance
• Faster access to data
• Faster access across a WAN link
• Access to objects in a set context (using bindery services)

Deleting a Replica

Deleting a replica removes the replica of the partition from a server.

If you want to remove a server from the directory tree, you can delete replicas from the server before removing it. Removing the replicas reduces the chance of having problems when removing the server.

You can also reduce synchronization traffic on the network by removing replicas. Keep in mind that you probably don't want more than six replicas of any partition.

You cannot delete a master replica or a subordinate reference.

If the replica you want to delete is a master, you have two options:

• Go to a server with another replica of the partition and make it the new master replica.

  This automatically changes the original master replica to a read/write replica, which you can then delete.

• Merge the partition with its parent partition.

  This merges the replicas of the partition with those of its parent and removes them from the servers they reside on. Merging removes partition boundaries, but not the objects. The objects continue to exist on each server which held a replica of the "joined" partition.

When you delete replicas, keep the following guidelines in mind:

• For fault tolerance, you should maintain at least three replicas of each partition on different servers.

• Deleting a replica deletes a copy of part of the directory database on the targeted server.

  The database can still be accessed on other servers in the network, and the server that the replica was on still functions in NDS.

  You cannot delete or manage subordinate reference replicas. They are created automatically on a server by NDS when the server contains a replica of a partition but not of that partition's child.

Changing a Replica Type

Change a replica type to control access to the replica information. For example, you might want to change an existing read/write replica to a read-only replica to prevent users from writing to the replica and modifying directory data.

You can change the type of a read/write or a read-only replica. You cannot change the type of a master replica, but a read/write or read-only can be changed to a master, then the original master is changed automatically to a read/write replica.

Most replicas should be read/write. Read/write replicas can be written to by client operations. They send out information for synchronization when a change is made. Read-only replicas cannot be written to by client operations. However, they are updated when the replicas synchronize.

You cannot change the replica type of a subordinate reference. To place a replica of a partition on a server which currently has a subordinate reference requires an Add replica operation. A subordinate reference replica is not a complete copy of a partition. The placement and management of subordinate reference replicas is handled by NDS. They are created automatically on a server by NDS when the server contains a replica of a partition but not of that partition's child.

You can't use this procedure to change the type of the master replica. To specify a new master replica, change the type of an existing read/write or read-only replica to master, and the original master replica is automatically changed to read/write.

Setting Up and Managing Filtered Replicas

Filtered replicas maintain a filtered subset of information from an NDS partition (objects or object classes along with a filtered set of attributes and values for those objects).

An administrator will generally use the filtered replica capability to create an NDS server that holds a set of filtered replicas that contain only the objects and attributes that will be synchronized to a non-NDS application or directory via the DirXML product.

To do this, ConsoleOne provides a snap-in with the ability to create a filtered replica partition scope and a filter. A scope is simply the set of partitions on which you want replicas placed on a server, while a replication filter contains the set of NDS classes and attributes you want to host on a server's set of filtered replicas. The result is an NDS server that can house a well-defined data set from many partitions in the tree.

The descriptions of the server's partition scope and replication filters are stored in NDS, and they can be managed through the Server object in ConsoleOne.

The Filtered Replica Configuration Wizard guides you step-by-step through the setup of a server's replication filter and partition scope.

Defining a Partition Scope

A partition scope is the set of partitions of which you want replicas placed on a server. The DirXML-Partition Scope window in ConsoleOne provides an expandable view of the hierarchy of partitions in the NDS tree. You can select individual partitions, a set of partitions of a given branch, or all of the partitions in the tree. You can then select the type of replicas of these partitions you want added to the server.

Viewing Replicas Present on an NDS Server

Adding a Filtered Replica to an NDS Server

Changing a Full Replica into a Filtered Replica

Setting Up a Server Filter

A server replication filter contains the set of NDS classes and attributes you want to host on a server's set of filtered replicas. You can set up a filter from any Server object. For filtered replicas, you can only have one filter per server. This means that any filter defined for an NDS server applies to all filtered replicas on that server. The filter, however, does not apply to full replicas.

A server's filter may be modified if required, but the operation generates a re-synchronization of the replica and may thus be time-consuming. Careful planning of the server's function is recommended.