2.4 Guidelines for Replicating Your Tree

Creating multiple eDirectory partitions does not, by itself, increase fault tolerance or improve performance of the directory. However, strategically using multiple replicas does. The placement of replicas is extremely important for accessibility and fault tolerance. eDirectory data needs to be available as quickly as possible and needs to be copied in several places to ensure fault tolerance. For information on creating replicas, refer to Section 6.0, Managing Partitions and Replicas.

The following guidelines will help determine your replica placement strategy.

2.4.1 Workgroup Needs

Place replicas of each partition on servers that are physically close to the workgroup that uses the information in that partition. If users on one side of a WAN link often access a replica stored on a server on the other side, place a replica on servers on both sides of the WAN link.

Place replicas in the location of highest access by users, groups, and services. If groups of users in two separate containers need access to the same object within another partition boundary, place the replica on a server that exists in the container one level above the two containers holding the group.

2.4.2 Fault Tolerance

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).

To create fault tolerance, plan for three replicas for each partition if the directory tree has enough servers to support that number. There should be at least two local replicas of the local partition. There is no need to have more than three replicas unless you need to provide for accessibility of the data at other locations, or you participate in e-business or other applications that need to have multiple instances of the data for load balancing and fault tolerance.

You can have only one master replica. Additional replicas must be read/write, read-only, or filtered. Most replicas should be read/write. 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 is 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.

Do not depend on a subordinate reference or filtered replicas for fault tolerance. A subordinate reference is a pointer and does not contain objects other than the partition root object. Filtered replicas do not contain all objects within the partition.

eDirectory allows for an unlimited number of replicas per partition, but the amount of network traffic increases as the number of replicas increase. Balance fault tolerance needs with network performance needs.

You can store only one replica per partition on a server. A single server can store replicas of multiple partitions.

Depending on your organization's disaster recovery plan, the major work of rebuilding the network after a loss of a server or location can be done using partition replicas. If the location has only one server, back up eDirectory regularly. Consider purchasing another server for fault tolerance replication.


  • Some backup software does not back up eDirectory automatically.

  • We recommend you exclude the DIB directory on your eDirectory server from any antivirus or backup software processes. Use the eDirectory Backup Tool to back up your DIB directory. For more information about backing up eDirectory, see Backing Up and Restoring NetIQ eDirectory.

2.4.3 Determining the Number of Replicas

The limiting factor in creating multiple replicas is the amount of processing time and traffic required to synchronize them. When a change is made to an object, that change is communicated to all replicas in the replica ring. The more replicas in a replica ring, the more communication is required to synchronize changes. If replicas must synchronize across a WAN link, the time cost of synchronization is greater.

If you plan partitions for many geographical sites, some servers will receive numerous subordinate reference replicas. eDirectory can distribute these subordinate references among more servers if you create regional partitions.

2.4.4 Replicating the Tree Partition

The Tree partition is the most important partition of the eDirectory tree. If the only replica of this partition becomes corrupted, users will experience impaired functionality on the network until the partition is repaired or the eDirectory tree is completely rebuilt. You will also not be able to make any design changes involving the Tree.

When creating replicas of the Tree partition, balance the cost of synchronizing subordinate references with the number of replicas of the Tree partition.

2.4.5 Replicating for Administration

Because partition changes originate only at the master replica, place master replicas on servers near the network administrator in a central location. It might seem logical to keep masters at remote sites. However, master replicas should be where the partition operations will occur.

We recommend that major eDirectory operations, such as partitioning, be handled by one person or group in a central location. This methodology limits errors that could have adverse effects to eDirectory operations and provides for a central backup of the master replicas.

The network administrator should perform high-cost activities, such as creating a replica, at times when network traffic is low.

2.4.6 Managing WAN Traffic

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.

If you are replicating the master replicas to a remote site or are forced to place replicas over the WAN for accessibility or fault tolerance, keep in mind the bandwidth that will be used for replication.

Replicas should only be placed in non-local sites to ensure fault tolerance if you are not able to get the recommended three replicas, increase accessibility, and provide centralized management and storage of master replicas.