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Defining a Replication Strategy
One of the more important reasons to replicate directory data is to balance the
workload of your network. When possible, you should move data to servers that
can be accessed using a reasonably fast and reliable network connection. The most
important considerations are the speed and reliability of the network connection
between your server and your directory users.
Directory entries generally average around one Kbyte in size. Therefore, every
directory lookup adds about one Kbyte to your network load. If your directory
users perform around ten directory lookups per day, then, for every directory user,
you will see an increased network load of around 10,000 bytes per day. Given a
slow, heavily loaded, or unreliable WAN, you may need to replicate your directory
tree to a local server.
You must carefully consider whether the benefit of locally available data is worth
the cost of the increased network load because of replication. If you are replicating
an entire directory tree to a remote site, for instance, you are potentially adding a
large strain on your network in comparison to the traffic caused by your users'
directory lookups. This is especially true if your directory tree is changing
frequently, yet you have only a few users at the remote site performing a few
directory lookups per day.
If your directory tree on average includes in excess of 1,000,000 entries, and it is not
unusual for about ten percent of those entries to change every day, then if your
average directory entry is only one Kbyte in size, you could increase your network
load by 100Mbyte per day. However, if your remote site has only a few employees,
say 100, and they are performing an average of ten directory lookups a day, then
the network load caused by their directory access is only one Mbyte per day.
Given the difference in loads caused by replication versus that caused by normal
directory usage, you may decide that replication for network load-balancing
purposes is not desirable. On the other hand, you may find that the benefits of
locally available directory data far outweigh any considerations you may have
regarding network loads.
A good compromise between making data available to local sites and overloading
the network is to use scheduled replication. For more information on data
consistency and replication schedules, refer to "Data Consistency," on page 111.
Example of Network Load Balancing
Suppose your enterprise has offices in New York and Los Angeles. Each office has
specific subtrees that they manage, shown in the figure.
Chapter 6
Designing the Replication Process
125
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