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The Sign-Off Table

Lesson 2 of 5

System conversion

9 min

A system conversion, often called brownfield, turns an existing SAP ERP system into an SAP S/4HANA system. SAP describes it as a complete technical in-place conversion: database, technical platform and application are moved in one step. Configuration, custom code and all historical data come along. It is technically possible from SAP ERP 6.0, and SAP does not require or recommend an interim move to ERP on SAP HANA first.

The tool chain

ToolWhat it does in a conversion
SAP Readiness Check for SAP S/4HANAAnalyzes the system early: relevant simplification items, add-ons and business functions, custom code impact, data volume, sizing and recommended Fiori apps
Maintenance PlannerChecks the system description and calculates the target stack and conversion path
Simplification Item CheckChecks which simplification items are relevant and whether data is consistent enough to convert; blocking issues must be fixed or exempted
Custom code analysisFinds custom code that must change because of SAP S/4HANA simplifications, using SAP's code check tools
Software Update Manager (SUM)Performs database migration, software update and data conversion; the Database Migration Option (DMO) combines them in one run

SAP tools in a system conversion. Exact steps depend on release and source system.

  1. PrepareReadiness Check, Maintenance Planner, cleanup of custom code and data volume, business partner synchronization
  2. CheckSimplification Item Check; fix consistency errors; adapt custom code
  3. Sandbox conversionsConvert copies of production repeatedly until the process is stable
  4. Technical conversionSUM: database migration to SAP HANA if needed, software update, data conversion
  5. Follow-upFinance data migration steps, mandatory configuration, custom code fixes, Fiori setup
  6. Test and cut overRegression and comparison tests; rehearsed conversion weekend
A system conversion from preparation to go-live.
The Sign-Off Table · thesignofftable.com/academy/sap-s4t-102

Preparation is business work too

Many conversion tasks happen in the old system, months before the technical conversion. Customers and vendors must be synchronized into business partners. Inconsistent financial data must be cleaned so that the finance conversion steps run. Data volume can be reduced by archiving. Simplification items need business decisions, for example how credit management will work in the new component. These tasks need key users and process owners, which is why a conversion is never "IT only".

Sandbox conversions and the dual landscape

Teams convert copies of production in a sandbox several times. Each run finds errors, fixes are recorded, and the run gets faster and cleaner, until the full sequence can be repeated predictably. Meanwhile the business keeps changing the live ECC system, so for some months the program runs a dual landscape: a maintenance line for production support and a project line for the conversion, with changes retrofitted from one to the other. Retrofit is a frequent source of defects and must be tracked and tested.

  1. Month 1 to 3Readiness and preparationReadiness Check, business partner synchronization, cleanup, code analysis
  2. Month 3 to 6Sandbox conversionsRepeated runs on production copies; fixes recorded; follow-up activities defined
  3. Month 6 to 9Development and quality conversionsCustom code adapted; configuration completed; integration and regression testing
  4. Month 9 to 11Production rehearsalsFull conversion rehearsals with timing; comparison and reconciliation tests
  5. Go-live weekendProduction conversionConverted, validated, signed off; old system state kept as fallback until sign-off
An illustrative conversion timeline. Real durations depend on size, complexity and downtime targets.
The Sign-Off Table · thesignofftable.com/academy/sap-s4t-102

Downtime

The technical conversion needs business downtime, and for large databases it can be long. SUM and DMO offer downtime-minimizing options, and SAP offers services for very large systems. Downtime is measured, not guessed: each production rehearsal times every step. The business then decides whether the window fits or whether downtime optimization is worth its extra complexity and testing. Contoso plans two mock conversions and a dress rehearsal in its systems CMD, CMQ and CMP, and the production conversion must fit a 60-hour window from Friday 18:00 to Monday 06:00, including validation and sign-off.

What would you do?

In Contoso's first sandbox conversion, SUM stops because the Simplification Item Check reports inconsistent data in finance. The technical team proposes skipping the check to keep the schedule. What should happen?

Key points
  • System conversion turns an existing SAP ERP 6.0 system into SAP S/4HANA in one step, keeping configuration, code and history.
  • Tools: Readiness Check, Maintenance Planner, Simplification Item Check, custom code analysis, SUM with DMO.
  • Preparation such as business partner synchronization and data cleanup is business work.
  • Repeated sandbox conversions, a dual landscape with retrofit, and measured downtime are typical.

Check your understanding · not graded

Lesson check

  1. 1. Which tool performs the database migration, software update and data conversion?

  2. 2. What does the Simplification Item Check report?

  3. 3. Why do teams run several sandbox conversions?

  4. 4. What is retrofit in a conversion project?