The short answer
For a warehouse, reporting database, data lake or high-volume operational database:
- InventoryEverything that reads or writes it, not just the data.
- Pick a patternOld and new run side by side.
- ReconcileCounts, totals and key reports, before switching.
- Cut overIn planned steps, with a tested rollback.
- DecommissionDeliberately, within retention and data protection obligations.
Skip inventory or reconciliation and reports or downstream systems quietly break after cutover.
Step 1: build an inventory
Data sets
Databases, schemas, tables, files: size, growth, owner.
Consumers
Reports, dashboards, notebooks, apps, exports, scheduled jobs reading it.
Producers
Applications, integrations and ETL jobs writing it.
Sensitivity
Personal, health, financial or confidential data sets.
Retention
How long each data set must be kept, and why.
Usage
What is really used; retire what nobody needs.
Discovery tools help: AWS describes DMS Fleet Advisor as building an inventory of servers, databases and schemas that could be migrated (AWS). Tools find databases; only the business knows which reports matter.
Step 2: choose a migration pattern
| Pattern | How it works | Suits |
|---|---|---|
| Big bang | Copy everything, switch everyone at once | Smaller platforms, tolerant users, a long quiet window |
| Phased by domain | One subject area at a time (finance data, then sales data) | Large platforms with clear domains |
| Parallel run with ongoing replication | Old and new stay in sync while consumers move gradually | Platforms that cannot tolerate downtime |
Parallel running needs change replication. AWS Database Migration Service supports one-time migrations and ongoing replication (AWS); other cloud providers and database vendors offer comparable tools.
Step 3: decide what changes and what does not
Adding redesign (new models, tools, naming) makes reconciliation harder: differences may come from the redesign, not errors. Migrate like for like first, then improve, or redesign one domain at a time against the old platform. Document every intended difference so nobody mistakes it for a defect.
Step 4: reconcile before you switch
Agree acceptance tests with the people who use the data, and automate them to rerun through the parallel period:
- Row counts per table and load
- Key totals (revenue, claims, quantities) by period
- Critical reports from both platforms
- Record spot checks chosen by users
- Slowest important queries
Step 5: plan the cutover
List every step, owner, duration and how to reverse it:
- FreezeNo schema changes before cutover.
- Final syncLast synchronisation and reconciliation.
- RepointReports, applications and integrations.
- CommunicateFollow the user communication plan.
Data protection, location and security
- Personal data stays subject to the Nigeria Data Protection Act 2023 (NDPA) throughout, including temporary copies and test environments. The NDPC enforces it, and its GAID 2025 sets out how it applies. A large migration of personal data is often a good reason for a data protection impact assessment.
- Transfers outside Nigeria need a recognised basis under the NDPA, such as adequate protection in the destination or appropriate safeguards (for example, contractual clauses); the organisation remains accountable. Record the basis and be open with individuals.
- Where the data lands: no major public cloud region is in Nigeria, so usually a local data centre (Lagos or Abuja, for example) or a region abroad, South Africa and Europe being nearest. Choose in line with NDPA transfer rules and sector rules (CBN for banks, NITDA guidelines for public institutions), and check backups, replicas, logs and support access too.
- Encryption and access: encrypt in transit and at rest, restrict migration tooling, delete temporary copies.
General information, not legal advice.
Controlling cost
Large migrations can surprise finance. Watch for:
- Two platforms during the parallel run
- Egress charges leaving a cloud or data centre
- Targets sized for peak, not normal load
- Storing data that should be archived or deleted
- Exchange-rate moves on dollar-billed cloud services
Set a planned end date for the parallel run and track it.
A worked example
Hypothetical example. A health maintenance organisation (HMO) runs an on-premises reporting database feeding finance reports, employer statements and an analytics team. The hardware is ageing and nightly loads now overlap the working day.
A low-risk plan: inventory every report and job; complete a data protection impact assessment and choose the target (a local data centre, or a region abroad with a documented transfer basis); move the data to a managed database with ongoing replication from the old platform; repoint the analytics team, then employer statements, then finance reports, reconciling each against the old platform; switch off the old database only after a full month-end has run cleanly on the new one.
Cutover checklist
- Inventory of data sets, consumers, producers, sensitivity and retention is complete.
- Migration pattern chosen and agreed with business owners.
- Intended differences between old and new are documented.
- Automated reconciliation checks run successfully on production-sized data.
- Critical reports compared and signed off by their owners.
- Cutover rehearsed, with timings recorded.
- Rollback trigger and procedure agreed and tested.
- Data protection review done: target location, transfers outside Nigeria, temporary copies.
- End dates set for the parallel run and old-platform decommissioning.
Limitations
Some constraints are beyond this guide: vendor licence terms, proprietary formats, application code tied to one database engine, regulatory approvals. Some platforms cannot run in parallel at all; then careful rehearsal matters even more.
Next step
Our cloud services and migration work covers planning, migration and validation. For analytics platforms, see data analytics and business intelligence; for smaller system migrations, preparing your data for a CRM or ERP migration.
Sources and further reading
Product capabilities and guidance change. These are the primary sources this article relies on, checked on the review date above.
- What is AWS Database Migration Service?, Amazon Web Services
This article is general information, not legal, accounting or security advice for your specific situation. Examples are hypothetical unless stated otherwise.