Chapter 6. Designing the Replication Process94Access Type Type Count Accesses per Day Total AccessesTotal 135 million (3,125/second)Table 6.2. Calculating Directory Server LoadIf the hardware that runs the Directory Servers supports 500 reads per second, at least six or sevenDirectory Servers must be used to support this load. For enterprises with a million directory users, addmore 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 theconsumer 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 asensuring 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 fordirectory lookups.6.3.8.3. Example Replication Strategy for a Small SiteExample 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 theprimary server is shut down for maintenance or hardware upgrades. Also, set up a DNS round-robinto improve LDAP connection performance in the event that one of the Directory Servers becomesunavailable.6.3.8.4. Example Replication Strategy for a Large SiteAs Example Corp. has grown, it retains its previous characteristics (as in Section 6.3.8.3, “ExampleReplication 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 duringnormal business hours.
