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Learning About Sub-Reference Replicas

Novell Cool Solutions: Feature

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Posted: 16 Jun 2004
 

Have you ever wondered about sub-reference replicas (subRefs) and how they are used by eDirectory? Here's a brief explanation from one of our eDirectory support experts to help you see how the pieces fit together.


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Basically, a subRef replica is just like a pointer used for making tree walking possible. A subRef will be placed on a server that has a replica of the parent partition but not the child partition. In this case, the server will automatically get a subRef of that child partition.

Normally one doesn't need to worry about subRefs. NDS/eDir handles these automatically. If it needs one on a server it will automatically create it, and also automatically remove it when it is no longer needed.

For example, picture this tree structure:


Root (Partition)
|
O=ACME (Partition)
|
-OU=NYC (Partition)
| |
| -OU=Sales
|
-OU=ORD (Partition)
|
-OU=Engineering

In this example, Root, ACME, NYC and ORD are all different partitions. Root is the parent partition to ACME. ACME is a child partition of Root but at the same time a parent partition for NYC and ORD. NYC and ORD are child partitions to ACME.

Suppose we have 3 servers, SRV1, SRV2 and SRV3. They all hold replicas of the partitions above according to the table below:

SRV1 SRV2 SRV3
Root M RW ...
Acme M SR RW
NYC M RW SR
ORD M RW SR

In this case we notice that SRV2 gets a subRef of ACME because it holds a replica of Root, and that SRV3 gets a subRef of NYC and ORD because it holds a replica of ACME.


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