Load Balancing Example for Messaging Server

The following table lists the estimates for CPU power for each logical Messaging Server component in the logical architecture. This table repeats the final estimation calculated in the section Update the CPU Estimates .

Table 5–6 CPU Estimate Adjustments for Supporting Components

Component	CPUs	Memory
Messaging Server(MTA, inbound)	2	4 GB
Messaging Server(MTA, outbound)	2	4 GB
Messaging Server(MMP)	2	4 GB
Messaging Server(Message Store)	2	4 GB

For this example, assume that during technical requirements phase, the following quality of service requirements were specified:

• Availability. Overall system availability should be 99.99% (does not include scheduled downtime). Failure of an individual computer system should not result in service failure.

• Scalability. No server should be more than 80% utilized under daily peak load and the system must accommodate long-term growth of 10% per year.

To fulfill the availability requirement, for each Messaging Server component provide two instances, one of each on separate hardware servers. If a server for one component fails, the other provides the service. The following figure illustrates the network diagram for this availability strategy.

In the preceding figure the number of CPUs has doubled from the original estimate. The CPUs are doubled for the following reasons:

• In the event one server fails, the remaining server provides the CPU power to handle the load.

• For the scalability requirement that no single server is more than 80% utilized under peak load, the added CPU power provides this safety margin.

• For the scalability requirement to accommodate 10% increased load per year, the added CPU power adds latent capacity that can handle increasing loads until additional scaling would be needed.