Directory Server is a network-intensive application. You can estimate theoretical maximum throughput using the following formula. Notice that this formula does not account for replication traffic.
max. throughput = max. entries returned/second x average entry size
Imagine that a Directory Server must respond to a peak of 5000 searches per second and that the server returns one entry per search. The entries have an average size of 2000 bytes. The theoretical maximum throughput would be 10 megabytes, or 80 megabits, not counting replication. 80 megabits are likely to be more than a single 100-megabit Ethernet adapter can provide. To improve network availability for a Directory Server instance, equip the system with a faster connection, or with multiple network interfaces. Directory Server can listen on multiple network interfaces within the same process.
The preceding example assumes that the client application requests all attributes when reading or searching the directory. Generally, you should design client applications so that they request only the required attributes.
If you intend to cluster Directory Servers on the same network for load balancing purposes, make sure the network infrastructure can support the additional load generated for replication. If you plan multi-master replication over a wide area network, test your configuration to make sure the connection provides sufficient throughput with minimum latency and near-zero packet loss. High latency and packet loss both slow replication. In addition, avoid a topology where replication traffic goes through a load balancer.