Subrefs: What Are They, and Why Do I Need Them?
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Posted: 21 Oct 2004
What are subordinate references (subrefs) and why do I need them?
An eDirectory Forum reader commented: "I have a small network with about 15 NetWare servers. We have 10 offices with a server in each and 6 servers in our headquarters office. When I designed the tree I split it into two OUs. One is called field and contains OUs for our various field offices. Each of these OUs has its own server that authenticates all logins and provides file and print services for that particular OU."
"While talking to Novell about a DS issue recently the tech told me I should split all these OUs into their own partitions. He suggested that I have one master and 2 read-write replicas for each of these new partitions. He suggested that I put the master and one of the read-writes at 2 different servers at our HQ site, and one of the R/Ws on the server for the particular OU.
I created the partition, and the master was created on the same server that had the Master of Root. All other servers had R/W replicas. I went to one of the servers that had a R/W created on it and deleted it. All of a sudden, a subordinate reference showed up. I have looked at trying to delete it, but can't see any way, at least not one that I am comfortable with. Is there a rule about subrefs? Do I need them? What do they do? Do servers with subrefs have to be in the replica ring?"
A Forum expert contributed the following helpful insights about subrefs ...
SubRefs are pointers to help servers walk to other partitions.
It is a bit like real life, in that the child partition will know where the parent partition is located (so it does not get an SR), but the parent partition does not know where the child may be (so it needs a pointer to where to go to talk to the child partition).
So, if a server holds a parent replica but not the child, it will have a SubRef pointing the way. If you need one of these pointers, it will be "automagically" created for you. If it is no longer needed, it will be removed.
Note that while this may be good "directory services" advice, it may not be good "licensing" advice. If you are not using an MLA type license, when your users log in their clients will insist on talking only to the Master replica (at your HQ site), and will ignore the local R/W replica holding server. If your WAN link is down, your users will not be able to log in.
If this applies to you, you may wish to modify your replica placement strategy so that the server that is local to the users has the Master, and your HQ servers hold the Read/Writes.
For another Cool Solutions article on subrefs, see: http://www.novell.com/coolsolutions/nds/features/a_subrefs_edir.html
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