Navigating SAP S/4HANA Migration Risks: Practical Challenges and Risk Management

Li Wei breaks down what you need to know

If you’re leading or supporting an SAP S/4HANA technical migration, you already know it’s more than a simple upgrade — it’s a complex transformation with many moving parts and risk factors. Yet, vendor marketing often glosses over the gritty realities, leaving practitioners scrambling when issues arise. I’ve been in the trenches guiding mid-to-large enterprises through these migrations and want to share a grounded view of the key challenges and how to manage them effectively, so you can avoid costly surprises and deliver measurable business value.

The Real Story

SAP S/4HANA migrations aren’t just about moving to a new database or system version. They affect data integrity, custom code, system availability, and infrastructure sizing in ways that can disrupt business operations if not carefully planned.

Data consistency and integrity issues are some of the most subtle yet impactful risks. During migration, data transformations and conversions happen behind the scenes. If your source data has inconsistencies — say, duplicate master records or incomplete transactional data — these can cause migration failures or corrupt your new system’s data model. For example, I once worked with a manufacturing client where inconsistent material master data led to a failed migration step in the finance module, requiring a rollback and re-cleaning of data.

Custom code compatibility is another major pitfall. Many clients underestimate the effort needed to adapt Z-code and enhancements to S/4HANA’s new data models and APIs. I’ve seen projects where over 70% of custom code required remediation, often creating delays and cost overruns. Blindly migrating custom code without this assessment risks system instability or functional gaps post-migration.

Then, there’s the cutover downtime and system performance impact. The technical migration — whether system conversion, landscape transformation, or new implementation — usually involves significant downtime. Without realistic downtime planning, you risk impacting critical business periods. Moreover, initial post-migration performance can degrade if the new landscape sizing and infrastructure aren’t properly aligned with workload demands.

Lastly, practitioners often overlook the technical prerequisites and landscape sizing for S/4HANA. The in-memory HANA database demands different hardware profiles and network setups compared to traditional SAP ECC landscapes. Underprovisioning can lead to bottlenecks and frustration, while overprovisioning inflates costs unnecessarily.

What This Means for You

Different roles on your project will face distinct challenges — here’s what to watch out for:

• Enterprise Architects: You must validate the overall migration approach aligns with business goals without overcomplicating the landscape. This means confirming that custom code remediation and data quality efforts are realistically scoped, and that fallback plans exist. Avoid vendor-driven “one-size-fits-all” blueprints; tailor your architecture based on your enterprise’s unique landscape and constraints.

• Basis Teams: Prepare early for system sizing and infrastructure readiness. Don’t just rely on SAP’s sizing reports — conduct load tests and simulate peak workloads post-migration. Also, invest time to understand the technical prerequisites like HANA-specific kernel patches, OS tuning parameters, and database backups strategies.

• Consultants (Functional & Technical): Focus on data cleansing well before migration. Use automated tools but supplement them with manual validation focused on business-critical master data and transactional datasets. For custom code, perform a thorough compatibility analysis using SAP’s SAP Readiness Check and Code Inspector tools, and plan for iterative code remediation cycles.

• Project Managers and Business Stakeholders: Be realistic about downtime windows and communicate early with business units. Factor in fallback time and the possibility of multiple cutover attempts. Also, budget for unexpected issues — migration projects rarely go 100% according to plan.

Action Items

• Conduct comprehensive data profiling and cleansing weeks or months before migration. Use SAP Data Services or third-party tools, and manually validate critical records.

• Run SAP Readiness Check and custom code analysis tools early to identify incompatible code and plan remediation resources.

• Simulate cutover downtime windows using sandbox or test environments to validate system performance and timing.

• Engage Basis teams to validate hardware and network sizing against expected S/4HANA workloads, including peak business cycles.

• Develop and test fallback and recovery plans. Don’t assume the migration will succeed on the first try; prepare rollback strategies with clear decision gates.

Community Perspective

From discussions with peers in SAP user groups and forums, several insights stand out:

• Many organizations underestimate the volume and complexity of custom code remediation, leading to schedule overruns.

• Data quality is often a “hidden” risk; teams focus on technical migration tools but neglect business data ownership and cleansing accountability.

• There is a tendency to trust vendor tools and reports without cross-validating results, resulting in surprises during cutover.

• Realistic downtime planning is a frequent source of tension between IT and business units; transparent communication and early engagement help alleviate this.

Bottom Line

SAP S/4HANA technical migration is not a magic button — it’s a high-stakes project requiring disciplined planning, honest assessment, and pragmatic risk management. Vendors provide useful tools and guidelines, but it’s up to you as practitioners to critically validate assumptions, rigorously test, and prepare fallback plans. Success depends on how well you manage data integrity, custom code adaptation, system sizing, and downtime impact — not just how quickly you execute the migration.

If you take away one thing from my experience: invest the time upfront to understand your unique technical landscape and business requirements deeply. That investment pays dividends in avoiding costly rollbacks, performance issues, and unhappy stakeholders down the line.

Source: Original discussion/article

References

• SAP HANA Platform Overview- SAP S/4HANA Product Information

References

• SAP S/4HANA Product Information
• SAP HANA Platform Overview
• What are the challenges of SAP S/4HANA migration