Recenlty I was involved in a project which was sort of SAP instance consolidation variety, coupled with partial greenfield implementation as a few divisions of my client was moving from usage of legacy system to full-fledged SAP. With regard to SAP systems we are actually moving from SAP 4.7 to ECC 6.
Basically this not an upgrade project but involving two different already existing SAP systems with SAP 4.7 moving to sunset. So the project involved data migration between two SAP systems. In this project major changes on business process and design happened only in the areas of production planning and Costing while all other areas the business processes just remained the same.
So the expectation was data migration should be pretty simple as both the systems are SAP and also barring two areas there is no change in the business process design except for obvious changes on organizational elements involving little rationalization on the number of organization elements.
But our experience turned out to be opposite. We found that we had to spend lot of design & development effort on taking care of data migration complexities due to the variations of data migration objects across the areas irrespective of whether there is a change in the business process or not. Particularly the objects under Plant Maintenance and Quality management turned out to be very difficult and we had to spend almost more than 2 to 3 times of the initial estimates.
Practically on a few objects we had to go back to business and revisit the requirements on some technically complex and difficult objects on their necessity for data migration as it is and/or migrate it in a simplified way. These sessions are very difficult ones as one can easily imagine on how to explain that we find data migration so difficult between SAP systems. From the business stakeholders perspective we are trying to manufacture complexity as it is just a download and upload of data. While such simplication can be dismissed as dumb argument, but it has a valid point that why data migration between two SAP systems should be complicated at all, given the business processes remaining the same.
While we have standard data migration tools like LSMWs, BAPIs etc., for data migration usage but I can confidently say it will be a rare project where these tools are used as it is without development and testing efforts. So the question begs answer is that can we not do data migration between two SAP systems by a simpler process like it is done on legacy systems.
Given that green field SAP projects have dried up and what we are going to have are projects like SAP instance consolidation due to mergers and acquisitions or SAP client splitting due to business diversifications etc., where-in both the source and destination will turn out to SAP systems. So the business stake holder expectation that data migration between such systems have to be simpler and cheaper is a very valid expectation.