This topic contains the following:
Creating multiple NDS partitions does not, by itself, increase fault tolerance or improve performance of the Directory. However, strategically using multiple replicas does.
Novell recommends at least three real replicas for each partition if the Directory tree has enough servers to support that number. 'Real' replicas means master, read/write, or read-only replicas (subordinate reference replicas are created and managed by NDS, not the administrator).
NDS replication provides:
If a disk crashes or a server goes down, replicas on servers in other locations can still authenticate users to the network and provide information on objects in partitions stored on the disabled server.
With the same information distributed on several servers, you are not dependent on any single server to authenticate you to the network or to provide services (such as login).
A single server can store replicas of multiple partitions.
NOTE: Directory replication does not provide fault tolerance for the file system. Only information about Directory objects is replicated.
To provide fault tolerance for your files, you must mirror or duplex your hard disks and enable the Transaction Tracking System* (TTS*) feature. TTS is enabled by default when the server is installed.
If users currently use a WAN link to access particular Directory information, you can decrease access time and WAN traffic by placing a replica containing the needed information on a server that users can access locally. However, in some cases, WAN traffic could increase due to the amount of synchronization required.
Distributing replicas among servers on the network allows quick and reliable access because information is usually retrieved from the nearest available server containing the specified information.
Add a replica of a partition to a server (and set bindery context appropriately) to allow users to access bindery services provided by NDS objects stored in that partition. Users will be able to access NDS objects providing bindery services only if real objects exist on that server. Adding a replica of a partition to the server adds real objects to the server and lets users with User objects in that partition log in to the server with a bindery connection. If a partition is not stored on a server, the Set Bindery Context command will fail for contexts in the partition.
You can add additional replicas of a partition, within these guidelines:
Most replicas should be read/write. Read/write replicas can be written to. They can handle object viewing, object management, and user login, just as the master replica can. They send out information for synchronization when a change has been made.
Read-only replicas cannot be written to. They allow object searching and viewing, and they are updated when the replicas of the partition synchronize.
Deleting a replica removes the replica of the partition from a server.
If you want to remove a server from the Directory tree, you could delete replicas from the server before removing it. Removing the replicas reduces the chance of having problems 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.
NOTE: You cannot delete a master replica or a subordinate reference replica.
If the replica you want to delete is a master, you have two options:
This automatically changes the master replica to a read/write replica, which you can then delete.
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:
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.
You can change the type of a read/write or a read-only replica. However, you cannot use a change replica type operation to change the master replica to a different type.
You cannot change the type of a master replica, but a read/write or read-only can be changed to a master---and the master will be 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 has been 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.