Challenges of Mainframe Modernization

Mainframe migration projects are complex and require close management of the process, budgets and timelines that have been set as project goals. A Reuse approach will involve rehosting (from unisys to Azure) and likely some re-engineering and refactoring to complete an entire mainframe migration. It will also involve data and file conversions for transitioning the database to the cloud.

As we’ve been emphasizing, the first challenge of any mainframe modernization project is to develop a rock-solid plan built upon a thorough application portfolio assessment and rationalization.   As you put your plan together and begin to execute, here are additional factors you’ll need to watch out for:


Many mainframe environments with large and complex application portfolios do not have documentation that details what these mainframe applications do, and how they do it. Many applications are decades old, so the original system, with changes likely every year, has become a maintenance nightmare. The external interaction with these systems, the Input/Output, is how these systems get defined to the business, and the rest of the system is just a black box.

Migrating a minimally-documented system of this nature is tricky and the testing prior to the “go live” deployment is critical to mitigating this issue. (And, of course, copious documentation should be captured for the resulting system.)

Application-Specific Challenges

There are a couple of general points about the application portfolio that should be noted. As mentioned above, the lack of documentation on these aging systems makes the migration effort more difficult. The project team that drives a migration project must then resort to “mining” the actual application source code to determine exactly the behavior of the application.

Another important application-specific issue for consideration is discovering the integration requirements and dependencies of the application with other systems and databases. These integrations and dependencies must be clearly identified and, if still needed, they must be re-connected (possibly rebuilt) and made operational along with the migrated system

Running Parallel Systems

For a short while, there may need to be some parallel processing between the mainframe application, while it is still being used in production, and the newly migrated system, on the new platform. Planning and executing this parallel processing will be a challenge, and will require extra time and attention to make it successful.

Another example of when you may choose to run parallel systems is if you want to achieve quick reductions in mainframe processing consumed by moving the development and test environments to an Azure-based emulator while keeping the production system on the mainframe for the interim.

Data Integrity

Moving the contents of large databases is very challenging on a number of levels. Typically, a database “cleanup” will be necessary to ensure that the contents of the new target database is as accurate, and as complete, as possible.

A mainframe modernization project is a good time to transform, correct and validate the organization’s data.

Speed to Completion

In almost every project, speed will be a top priority. The costs and complexities of extended project cycles can have an enormous negative impact in tangible and intangible terms.  As project cycles get extended, staff attrition can become a big issue and staff fatigue may also become a factor.

Paying for a continuation of the primary production system and funding the development efforts of the new system at the same time will have a temporary financial impact for as long as that duality continues. Getting to a “go live” status quickly and efficiently with the new system, and retiring the old system, will keep unexpected costs to a minimum.

Project Funding

It is very important for any modernization project to be properly funded and supported by the business management team and the executives. This support is essential to maintain project continuity and funding throughout the project cycle. Since we stated earlier that speed will be a factor in the project execution, funding must be in place to sustain that speed.


Mainframe migration projects come in many forms. In every case, a variety of specialist skills will be needed on the project team. These specialists may include business analysts working to mine and understand the business rules embedded in the legacy applications.

It will also include experts in specific programming languages, databases, networks, terminal devices and many other components of the total application portfolio that will need to be addressed over the course of the migration to the target platform. Staff must also be available to address any specific functionality or use case of the mainframe application environment.

All this technology must be transferred to the equivalent functionality on the target cloud platform and work as it did in the original mainframe environment. Thorough testing by the project team, followed by testing amongst the business users of the original mainframe application system, is an absolute requirement. Once testing is completed, a final performance and tuning (P&T) exercise will ensure that the new cloud deployment is performing at optimal levels.

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