Defining a Replication StrategyChapter 6 Designing the Replication Process 133Example of Load Balancing for Improved PerformanceSuppose that your directory must include 1,500,000 entries in support of 1,000,000users, and each user performs ten directory lookups a day. Also assume that youare using a messaging server that handles 25,000,000 mail messages a day and thatperforms five directory lookups for every mail message that it handles. Therefore,you can expect 125,000,000 directory lookups per day just as a result of mail. Yourtotal combined traffic is, therefore, 135,000,000 directory lookups per day.Assuming an eight-hour business day, and that your 1,000,000 directory users areclustered in four time zones, your business day (or peak usage) across four timezones is 12 hours long. Therefore you must support 135,000,000 directory lookupsin a 12-hour day. This equates to 3,125 lookups per second (135,000,000 /(60*60*12)). That is:Now, assume that you are using a combination of CPU and RAM with yourDirectory Servers that allows you to support 500 reads per second. Simple divisionindicates that you need at least six or seven Directory Servers to support this load.However, for enterprises with 1,000,000 directory users, you should add moreDirectory Servers for local availability purposes.One method of replication is to:• Place two Directory Servers in a multi-master configuration in one city tohandle all write traffic.This configuration assumes that you want a single point of control for alldirectory data.• Use these supplier servers to replicate to one or more hub suppliers.The read, search, and compare requests serviced by your directory should betargeted at the consumer servers, thereby freeing the supplier servers to handlewrite requests. For a definition of a hub supplier, refer to “CascadingReplication,” on page 121.1,000,000 users 10 lookups per user = 10,000,000 reads/day25,000,000 messages 5 lookups per message = 125,000,000 reads/dayTotal reads/day = 135,000,00012-hour day includes43,200 secondsTotal reads/second = 3,125
