Structuring the Migration for Best Results

When structuring the migration, the end goal is to move to the new platform without disrupting current services or losing functionality. The only way to be sure that service and functionality will not be lost during the migration is to perform lab testing. Having a fallback plan and solid disaster-recovery processes are also essential when planning the Exchange Server 2003 deployment. By breaking the migration into sections, the organization can move cautiously through the migration without making too many changes at one time. The following best practices deploy Exchange Server 2003 by migrating each service type at a time. For many smaller remote locations, this might not be feasible and all services might have to be migrated at the same time. Migrating by service type is usually the best solution for corporate sites and large remote offices.

Single Site Exchange 5.5 Migrations

Within the same Exchange 5.5 site, administrators have the flexibility of moving users between servers. Single-site Exchange 5.5 installations become a single Administrative Group with a single Routing Group when converted to Exchange Server 2003. If granular message routing is needed, additional Routing Groups can be added and servers within the Administrative Group can be moved to new Routing Groups after the conversion to Native Mode.

Because servers cannot be moved between Administrative Groups even after the conversion to Native Mode, administrators need to examine whether a single Administrative Group will fulfill the organization's administrative needs. Additional Administrative Groups can be added to the organization, but only by installing new Exchange Server 2003 systems. Users can be moved between Administrative Groups by moving the mailbox from group to group, but only after the switch to Native Mode.

Multisite Exchange 5.5 Migrations

Multisite migrations are a bit more complex than single-site migrations because an Exchange Server 2003 system must be established in each Exchange 5.5 site. After the first Exchange server is installed, administrators can use the Move Mailbox method to migrate users to Exchange Server 2003.

After the migration, the organization will contain multiple Administrative Groups with a single Routing Group in each that matches the Exchange 5.5 configuration. Even after the conversion to Native Mode, the servers in each site cannot be moved between Administrative Groups, so administrators need to examine whether this design will still work for the organization.

Understanding why the multiple sites were established might help in deciding how to handle the multiple sites. If the decision to have multiple sites was to originally delegate control of administration, the multiple Administrative Groups might still be needed. If multiple sites were implemented to control message flow and directory replication, consolidating many of the Administrative Groups might be desired.

Multiorganization Exchange 5.5 Migrations

Multiorganization environments must consolidate to a single Exchange Server 2003 organization to migrate to Exchange Server 2003 unless the organization plans to support multiple Active Directory forests. Multiple organization environments have the following choices when moving to Exchange Server 2003:

• Select one organization to be migrated to Exchange Server 2003 Use the most heavily populated organization if it fits the company's standards. Create new Exchange Server 2003 mailboxes for users in the other organization. Use ExMerge to move user data from the abandoned organization to Exchange Server 2003.

• Start with a clean Exchange Server 2003 organization and do not migrate either organization Both organizations feel equal pain that might be politically acceptable. Look at the ExMerge utility to migrate user data, or run both Exchange 5.5 organizations for a short period of time and allow users to forward mail to their Exchange Server 2003 mailbox.

• Use the Move Server Wizard to collapse one organization into the other before migrating Use the company-standard organization for the organization to be migrated to Exchange Server 2003. Merge the other organization into it before migrating through the Move Server Wizard. No one loses mail during the migration, but it might be a hard sell politically.