Once the decision has been taken to migrate away from a legacy environment, the primary business challenge is business continuity. Since many of these applications are mission critical, running various aspects of the business, the migration strategy has to ensure continuity to the new application — and in the event of failure, rollback to the mainframe application. This approach requires data in the existing application to be synchronized with data on the new application.

Making the challenge of data migration more complicated is the fact that legacy applications tend to be interdependent, but the need from a risk mitigation standpoint is to move applications one at a time. A follow-on challenge is prioritizing the order in which applications are to be moved off the mainframe, and ensuring that the order meets both the business needs and minimizes the risk in the migration process.

Once a specific application is being migrated, the next challenge is to decide which business processes will be migrated to the new application. Many companies have business processes that are present, because that's the way their systems work. When migrating an application off the mainframe, many business processes do not need to migrate. Even among the business processes that need to be migrated, some of these business processes will need to be moved as-is and some of them will have to be changed. Many companies utilize the opportunity afforded by a migration to redo the business processes they have had to live with for many years.

Data is the foundation of the modernization process. You can move the application, business logic, and work flow, but without a clean migration of the data the business requirements will not be met. A clean data migration involves: