CLUSTERS

Example of clustering three servers for mail and applications
If you have three servers available in the cluster, distribute databases across the three servers. In this scenario, you should replicate critical databases to every server in the cluster. You should replicate non-critical databases to only one other server or to no other server at all. In addition, distribute mail databases equally across the cluster servers. To ensure balance in case of failover, each server should contain replicas of half of the mail databases of each of the other servers. In that way, if a server becomes unavailable, the mail workload of that server is equally divided between the other two servers.

In the following figure, each server contains a replica of the critical databases, DB1 and DB2. There are fewer replicas of the other databases because they are less critical. In addition, each server contains 100 mail databases. Therefore, each server should contain replicas of 50 mail databases from each of the other servers.

Three-server cluster for mail and applications