SAP proposes different strategies to migrate an SAP ECC to S4HANA:
(a) Greenfield: Start from scratch, with an empty system in which the business processes were configured according to the company's requirements.
b) Brownfield. It is a conversion that involves retaining the database from the ECC system, to the new data dictionary in full form. The configuration of the processes that may be modified during the implementation phase is also converted.
c) Bluefield: A subset of the data from the ECC database is copied to a S4HANA with a new business process configuration.
In each scenario, you have to evaluate and decide what to do with the data.
Greenfield: What do we do with the data left in the legacy ECC? Based on the fact that much of this data is relevant to the business and therefore must be accessible, a reasonable solution in terms of cost and complexity must be sought. In this case, it is advisable to consider what is called “system decommissioning”. This consists of storing the relevant information in an accessible format. Ideally, this information should be accessible from the new S4HANA.
Bronwfield: This is the classic scenario that forces us to consider data archiving as a fundamental tool to significantly lower HANA infrastructure costs and at the same time optimize migration downtime, which also translates into very significant costs.
Bluefield: As it is a selection of data that will be copied to the new S4HANA, the same reasoning applies as in the case of Greenfield. We must consider a decommissioning solution to keep the data that are not replicated at reasonable costs.
Each of these scenarios derive in particularities and conditions that are specific to each company. We can help you find the best solution for the type of migration you have decided to undertake.