If the hardware that runs the Directory Servers supports 500 reads per second, at least six or seven Directory Servers kust be used to support this load. For enterprises with a million directory users, add more Directory Servers for local availability purposes.

There are several different methods of replication:

•Place two Directory Servers in a multi-master configuration in one city to handle all write traffic.

This configuration assumes that there should be a single point of control for all directory data.

•Use these supplier servers to replicate to one or more hub suppliers.

The read, search, and compare requests serviced by the directory service should be targeted at the consumer servers, thereby freeing the supplier servers to handle write requests.

•Use the hub supplier to replicate to local sites throughout the enterprise.

Replicating to local sites helps balance the workload of the servers and the WANs, as well as ensuring high availability of directory data.

•At each site, replicate at least once to ensure high availability, at least for read operations.

•Use DNS sort to ensure that local users always find a local Directory Server they can use for directory lookups.

6.3.8.3Example replication strategy for a small site

Example Corp. has the following characteristics:

•The entire enterprise is contained within a single building.

•The building has a very fast (100 MB per second) and lightly used network.

•The network is very stable, and the server hardware and OS platforms are reliable.

•A single server is capable of easily handling the site's load.

In this case, Example Corp. decides to replicate at least once to ensure availability in the event the primary server is shut down for maintenance or hardware upgrades. Also, set up a DNS round-robin to improve LDAP connection performance in the event that one of the Directory Servers becomes unavailable.

6.3.8.4Example replication strategy for a large site

As Example Corp. has grown, it retains its previous characterstics (as in “Example replication strategy for a small site”) with a few changes:

•The enterprise is contained within two separate buildings.

•There are slow connections between the buildings, and these connections are very busy during normal business hours.

As their network needs changes, then Example Corp.'s adminsitrators adjust their replicaiton strategy:

•Choose a single server in one of the two buildings to contain a master copy of the directory data.

This server should be placed in the building that contains the largest number of people responsible for the master copy of the directory data. We shall refer to this building as Building A.

•Replicate at least once within Building A for high availability of directory data. Use a multi-master replication configuration to ensure write-failover.

•Create two replicas in the second building (Building B).

•If there is no need for close consistency between the supplier and consumer server, schedule replication so that it occurs only during off-peak hours.

6.3 Defining a replication strategy

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