Design a Data-Migration Plan: Legacy Payroll to New Platform

Context

You are responsible for migrating a legacy payroll system to a new platform in a large, regulated environment. Payroll data contains sensitive PII and must remain accurate and compliant across jurisdictions. The migration must avoid missed paydays, tax filing errors, and financial reporting discrepancies while integrating with HRIS, time/attendance, banking, benefits, GL, and tax reporting.

Task

Propose an end-to-end migration plan that covers:

1. Migration approach and phases
   • Compare phased vs. big-bang migration and recommend when to use each.
   • Define major phases and key deliverables.
2. Data mapping and transformation
   • Canonical data model, code mapping, historical data scope, and ID strategy.
3. Data validation and reconciliation
   • Controls, metrics, and acceptance criteria to ensure payroll accuracy.
4. Risk mitigation
   • Top risks, controls, and compliance considerations for payroll data.
5. Rollback and fallback strategies
   • Clear triggers, steps, and SLAs if a cutover fails.
6. Cut-over timing
   • Go/no-go criteria, freeze windows, and hour-by-hour playbook.
7. Stakeholder communication and governance
   • Who needs to know what and when; RACI and decision forums.

Hints: Consider phased vs. big-bang migration, parallel-run periods, and compliance requirements for payroll data.