Migrating to SAP S/4HANA is one of the most structuring transformation projects a company can undertake. The end of SAP ECC maintenance will begin in 2027 and end in 2030 at the latest - the countdown is on.
But even before launching the project, a strategic question needs to be asked: which migration trajectory should be chosen? Greenfield, Brownfield, Bluefield (Selective Data Transition) or Landscape Transformation - each approach responds to different contexts, objectives and constraints. Choosing the wrong approach at the outset means risking additional costs, uncontrolled delays and an incomplete transformation.
As Marc Cibert, IS & HR Project Director, reminds us, there's a fundamental truth to keep in mind:
"An ERP project, by definition, is a corporate project that will materialize in the form of the implementation of a system to support business processes. This is absolutely not specific to S/4HANA, but it is the first condition for having a chance of succeeding with the project: starting out in this frame of mind."
In this guide, our specialized SAP consultants present thefourmigration approaches, the key steps according to the SAP Activate methodology, the success factors and the classic mistakes to avoid.
For several years, FocusTribes has been supporting companies of all sizes in their SAP S/4HANA transformation projects, by providing expert freelance consultants, selected by co-optation and accredited through a strict validation process.
Marc Cibert has extensive experience in managing major IS transformation programs, and acts as program director on large-scale S/4HANA projects. He has himself been a principal on SAP projects managed with FocusTribes consultants.
Marcela Varela is currently Project Manager for Finance and Controlling at a FocusTribes customer implementing S/4HANA in Greenfield mode. She brings an expert field vision of S/4HANA's Finance specificities.
Vincent Duminy worked for FocusTribes with a major customer in the finalization phase of an S/4HANA pilot, designed to prove that the solution could meet the group's business needs and support functions before large-scale deployment.
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Before embarking on an implementation project, it's essential to understand the different possible paths.
|
Criteria |
Greenfield |
Brownfield |
Bluefield (SDT) |
Landscape Transfo. |
|
Definition |
Complete new installation - blank page |
Technical conversion of existing SAP ECC |
Hybrid approach, selective migration |
Restructuring of SAP landscape (mergers, spin-offs) |
|
Recovery of historical data |
No (or very partial) |
Yes - complete |
Partial - as desired |
Depending on scope |
|
Transfer of customizations (Z) |
No - replaced by SAP standards |
Yes - retained |
Partial |
Depending on scope |
|
Transformation opportunity |
Maximum |
Limited |
Medium to high |
Variable |
|
Project duration |
18 to 36 months |
6 to 18 months |
12 to 24 months |
24 to 48 months |
|
Complexity |
High |
Medium |
High |
Very high |
|
Cost |
High |
Lower cost |
Medium to high |
High |
|
Use cases |
Complete overhaul, first SAP, carve-out |
Rapid release, tight budget |
Keep some processes, transform others |
Mergers & acquisitions, multi-system consolidation |
The Greenfield vs Brownfield question is often posed as a binary choice. In reality, the answer depends above all on the company'ssituation. Vincent Duminy, SAP FI CO PS Expert Project Manager, explains:
"The big difference is process redesign: do I keep my business processes, or do I need to redesign them for various business reasons? Greenfield is process redesign, Brownfield is process retention. It's not one against the other, it's in relation to my business project, in relation to my transformation paradigm."
An important technical clarification: there's no such thing as a purely technical upgrade from SAP ECC to S/4HANA. Even in Brownfield, functional changes are unavoidable, notably in the accounting plan, BusinessPartner management or Copa structure. Vincent Duminy is categorical:
"There's no such thing as a purely technical upgrade. We're already in Brownfield, even if we say to ourselves 'I'll take my SAP ECC and put it in S/4HANA'. There will still be processes to overhaul. That's why we've opted to say: it's either Greenfield or Brownfield - there's no such thing as a purely technical upgrade."
|
Greenfield |
Brownfield |
|
|
Business processes |
Complete overhaul of processes |
Retention of existing processes |
|
Data recovery |
Easier (blank page) |
Complete, but major retrofit effort |
|
Time & Cost |
Longer and more costly |
Theoretically shorter and less costly |
|
Change management |
Major effort - new processes and new Fiori interface |
Limited but not zero impact (Fiori, new FI/CO paradigms) |
|
Recommended when... |
External growth, heterogeneous IS, processes to be harmonized, carve-out |
Stable processes, integrated system, tight budget |
The Greenfield approach is recommended when :
Marc Cibert sums up the market trend as follows:
"Most of the projects I've seen so far, whatever the ERP - I've done it on Oracle, I've participated on SAP - have ended with a Greenfield. Because it's always the process part, the business part, that has taken over from the technical issues."
Before embarking on a Greenfield project, it's essential to understand the real breaks between SAP ECC and S/4HANA. This evolution is structured around three major new features.
SAP Fiori completely replaces SAP ECC's transactional interface. Gone are the drop-down menus and transaction codes - users now access SAP via tiles that can be activated on any medium (PC, tablet, smartphone). Vincent Duminy explains the concrete impact:
"The big difference with Fiori is that you'll have to activate tile by tile. When it came to authorizations in ECC, we tended to give menus to users and restrict them. With Fiori, you'll have to give the menus to users on a tile-by-tile basis and select the appropriate authorizations. That's the big difference on the interface."
SAP S/4HANA is based on the in-memory HANA database, which eliminates the boundary between transactional (OLTP) and business intelligence (OLAP). Data is queried in real time directly at source, without intermediate tables or aggregations - what SAP calls the "no more aggregates" principle.
This is undoubtedly the most important breakthrough for Finance and Controlling teams. Marcela Varela, SAP FI CO S/4HANA Expert, explains:
"There are no longer any boundaries between FI and CO, between general accounting and cost accounting. Everything will be in the same table - the famous ACDOCA table, the Universal Journal. We're going to end up with a system where we don't have analytical object allocations, but rather account keys. That's where the big revolution comes in: the complete merging of general and cost accounting."
The concrete benefits are considerable for the teams who used Copa analytique in SAP ECC:
"For customers who were moving from ECC to S/4HANA and who were used to using Copa analytics, they're thinking: that's great, I don't have my gap anymore! We can be sure that the figures we're going to report at statutory level and at analytical management level are the same. And that's a huge advantage, it's what's most appreciated."
Material Ledger is also enabled by default in S/4HANA.Vincent Duminy adds:
"Copa accounting is enabled by default in S/4HANA - there's no reason to have Copa analytics anymore. And the Material Ledger is also activated by default. All this is now integrated, so we have far fewer reconciliation problems."
Beyond the technical aspects, user adoption is central. Marcela Varela shares her experience in the field:
"That's the big surprise: it's the user interface that changes completely. There are some very curious people who are very happy - 'I don't have to memorize the transaction code anymore'. And there are others who have a bit more trouble. But once they've gone through it, they say to themselves: 'Actually, it's great, I've got more information. It's a pretty positive change in the experience I've had."
SAP recommends the SAP Activate methodology for structuring S/4HANA projects. It is broken down into 6 distinct phases, which have replaced the former ASAP methodology.
This is the strategic scoping phase. It defines the functional scope (SAP modules: FI, CO, MM, SD, PP, HR, PS...), builds the business case, estimates the overall budget and selects the required consultant profiles.
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Focus - Shortage of SAP S/4HANA resources
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The preparation phase lays the organizational foundations: setting up project teams, establishing governance (steering committee, project committee), launching the change management plan. Marc Cibert insists on dedicated teams:
"I strongly advocate dedicated business teams. When you explain to a manager that his key users are going to spend 30% of their time on the project... you lose out. In reality, the 30% should be 100%. For me, dedicated business teams are fundamental in every functional area."
This is the intellectual heart of the project. SAP consultants and business teams work together to analyze target business processes during design workshops, identify gaps between SAP standards and business needs, define residual specific developments, and validate the Core Model - the target process model that will serve as a reference for the entire deployment.
The Realize phase is the technical site: configuration of the SAP system according to the validated Core Model, specific developments (ABAP, SAP BTP, interfaces), migration of masterdata, and unit testing. Marc Cibert is adamant about data migration:
"Data recovery is always an extremely complicated subject, extremely time-consuming and extremely risky in terms of the project's success or failure. You need a dedicated data recovery team and the tools to industrialize and speed up the process."
Before go-live: user tests (UAT), performance tests, end-user training in SAP Fiori and the new processes, and cutover plan.Marc Cibert on testing:
"Testing is fundamental. Unfortunately, it's often at the end of the chain - we're behind schedule, but we still want to get started on time. We're going to do one week less of testing... Bad idea. Bad idea. Bad idea again. Every time we think we're saving money by backlinking a phase, we'll pay 10 or 100 times more for it in production."
The go-live is not the end of the project. The Run phase includes: hypercare support (team reinforced over the first few weeks), KPI monitoring, post go-live optimizations, and setting up a release process for future changes. Marc Cibert underlines a point often overlooked in multi-entity deployments:
"In the case of deployments, you need to be prepared to have a team that continues to look after entities during the course of the project, and one that looks specifically at those already in production. Otherwise you have a central team completely torn between the two."
A Greenfield project cannot be managed by the IT department alone. It must be supported by senior management. Marc Cibert:
"Strong sponsorship is key to the success of any project. When I was a young consultant, we used to say: if you don't have a sponsor who is identified, motivated and available to go with you - don't go. Quite simply."
Governance must be defined even before the project starts: who decides what, at what level, within what timeframe? An experienced SAP project manager is essential for operational management and risk monitoring. Beware, too, of competing projects, as Marc Cibert points out:
"Beware of competing projects. In companies undergoing transformation, you may be confronted with projects for the implementation of shared services, or reorganizations in entities which will mean that you will no longer have business contacts. All this needs to be seen in a global way to avoid problems during the project."
Migration of master data (items, suppliers, customers, cost centers, etc.) is almost always the most time-consuming and riskiest project. You need to start auditing and cleansing data well before the Realize phase, ideally as early as the Explore phase.
Resistance to change is one of the primary risk factors on a Greenfield project. Marcela Varela shares her view from the field:
"There's an unlearning of what we knew about SAP. But let me reassure you: the basis, the fundamentals, the core functionality of ECC can also be found in S/4HANA. But yes, there are paradigm shifts that mean you're going to have to adapt. That's where the change management effort is going to come in."
"An SAP consultant is someone who knows the business and is capable of supporting your teams in all phases of the project, but who is also capable of getting information from the integrator and challenging it. And don't delay - the shortage of resources isn't going to get any easier in the coming months." -Marc Cibert, IS Project Director & HR Director
Marc Cibert quotes Albert Einstein in his presentation, "The definition of insanity is doing the same thing over and over again and expecting a different result." We've known about these mistakes in ERP projects for 20 years. And yet...
This is the fundamental error. A Greenfield SAP S/4HANA project is a business transformation project. The IT Department is the technical pilot, but responsibility for success lies with all the business departments.
"Data recovery is never purely a data recovery project. You'll always have functional issues. Even if you say 'I want to do exactly what I've got in my ECC in S/4HANA', you'll be faced with functional issues. It can never be purely technical." -Marc Cibert, IS & HR Project Director
The temptation to reproduce all the specifics of the old system in the Core Model is a classic trap. Marc Cibert formulates the rule of balance:
"The recommendation is to use mainly standard functionalities. Don't do anything specific because it's a pain in the ass to maintain. But I've never known a situation where we didn't have to make a few adaptations because the business required it. You just have to be careful that the requests are really specific to the business and not requests for comfort."
"We often forget the reporting stages in our processes. There isn't a manager in a finance department who doesn't need a report to make decisions. And the editors will explain that you have all possible reports as standard... except that they're never the ones you need." -Marc Cibert, IS & HR Project Director
UAT tests carried out too quickly, too late, with incomplete test scenarios lead to anomalies discovered post go-live.. Marc Cibert recommends a dedicated lead for the entire testing phase, with complete processes from start to finish, integrating migrated data, interfaces and reporting.
"I've done a lot of projects on different types of tools, and we've never or almost never respected the initial workload plan. But at least you shouldn't underestimate it. Because here too, false savings come back to bite us in the ass."- Marc Cibert, IS Project Director & HR Director
The duration varies between 18 and 36 months, depending on the size of the company, the number of SAP modules, the geographical scope and the complexity of the processes. For an SME with an FI/CO + MM + SD scope, a project lasting 12 to 18 months is realistic. For a large multi-country group, a minimum of 24 to 36 months is required.
Greenfield involves starting from scratch with a new installation of SAP S/4HANA, without taking over the configurations or specific developments of the old SAP ECC system. Brownfield is a technical conversion of the existing system, while preserving existing processes. There's no such thing as a purely technical upgrade: even with Brownfield, functional changes are inevitable (chart of accounts, BusinessPartners, Copa).
Bluefield (Selective Data Transition) is a hybrid approach: we choose precisely which data objects and processes are migrated from the old system, and which are rebuilt from scratch. It's more flexible than pure Greenfield, but also more complex to manage.
The Greenfield approach is recommended when: your SAP ECC is highly customized (numerous specific developments), you wish to overhaul your business processes in depth, you are integrating companies with heterogeneous information systems, you are in a carve-outsituation, or you are starting a first ERP implementation.
The two areas most impacted are Finance (FI/CO) with the merging of the Universal Journal ( ACDOCA table), the new Copa accounting model and the Material Ledger activated by default, and Supply Chain (MM, SD, PP) which benefits from the new real-time capabilities of the HANA database.
Yes, SAP offers both SAP S/4HANA Cloud Public Edition and SAP S/4HANA Cloud Private Edition. The Greenfield approach is particularly well-suited to the cloud, as it enables you to start out on a cloud-native architecture without any technical legacy. Please note: the functional differences between on-premise and cloud versions are significant and evolve with each release.
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