In a single-tiered architecture, there is no separation between access and data layers. The MTA, Message Store, and sometimes the Directory Server are installed in one layer. Figure 10–2 shows a single-tiered architecture.
Single-tiered architectures have lower up-front hardware costs than two-tiered architectures. However, if you choose a one-tiered architecture, you need to allow for significant maintenance windows.
Size your message stores like you size message stores in a Two-tiered Messaging Server Architecture.
Add CPU for SSL, if necessary.
Add more disks for the increased number of SMTP connections.
Add more disks for outbound MTA routing.
For specific instructions on sizing Messaging components in single-tiered or two-tiered architectures, contact your Sun Client Services representative.