As mentioned in previous posts, modernizing mainframes is a necessity, not an option. So now the question is, how should you embark on modernization?
Well, there are basically three choices: mainframe upgrading, source code rewriting, and mainframe rehosting. The below describes each of these three options.
Mainframe upgrading: This option is just kicking the can down the road. What you are basically doing is upgrading an outdated mainframe system to the newest version of the mainframe. You would get more capacity and performance, but you would also incur higher licensing costs. Most importantly however, the biggest problem of selecting this option is that you are resolving the single most important reason for modernization which is moving to an open system.
Source code rewriting: This option is basically a complete reconstruction of the existing system. Not only are you replacing hardware, but you are rewriting code from scratch. This poses two serious issues: loss of business logic, and instability of mission-critical services. Completely overhauling the existing source code means decades worth of valuable business logic which form the backbone of enterprises. As well, if you rewrite code from scratch, not only will it take many years to complete, there also is no guarantee of success. For companies that value seamless operation and keeping business logic, this option simply will not work for them. In fact, it would be better to just continuously upgrading their mainframe system.
Mainframe re-hosting: What is mainframe rehosting? It can be described as a “lift and shift” approach to modernization. You simply migrate your legacy applications and data to the open system made up of x86 servers, and then replace middleware, operating system, and database with their equivalents in the open environment. With this approach, you preserve your enterprise’s valuable business logic as well as keep on running your system as if it were running on the mainframe, all the while moving your system to the open environment thereby leveraging the newly found ability to easily integrate the newest technologies. Furthermore, this approach greatly reduces total cost of ownership (TCO) as well as allowing you to complete modernization in a fraction of the time it would take to do the same via source code rewriting. Lastly, there is no risk to system stability as application and data remain unchanged. Basically, if your legacy system is rehosted, it allows you to enjoy most of the benefits of modernization, but with little cost and risk.
As you can see, for most enterprises, the best way to embark on legacy modernization is to re-host your legacy system which resides in the closed system to the open system.