Data Migration Strategies
Backfill, dual-write, reconciliation and verification.
5 to work through
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beginner
A 6 TB order history must be backfilled into a new store before cutover. The link sustains 1 Gbps and the target ingests about 40 MB/s per writer. Roughly how long is the backfill, and which assumption decides whether it fits one weekend?
2 min answer -
advanced
A platform must migrate very large volumes of file data between storage systems. Which strategies apply, and what dominates the schedule?
2 min answer -
advanced
A shipping platform must migrate years of order and tracking data to a new store. What strategy handles both the historical bulk and the ongoing changes?
2 min answer -
advanced
Month 1 of a migration, the reference tables for currency and tax class are copied to the new store and verified row for row. Month 9, a regulator forces a new tax class into the legacy system. Month 11, the new system starts rejecting about 1 order in 400 with a validation error nobody can reproduce in test. What failed, and which design decision made it possible?
3 min answer -
advanced
The source data contains records that violate the target's constraints. How do you handle it and who decides?
2 min answer
3 terms in this topic
Data Migration Strategies
Moving data between systems with different models — where the difficulty is meaning and quality rather than transfer.
patternDual Write
Writing the same change to both the old and new stores during a migration, and the reconciliation that makes it trustworthy.
conceptReference Data Drift
The divergence between a source system's lookup tables and the copy taken at the start of a long migration, which turns into silent transaction rejec…
Neighbouring topics
Legacy Modernization
General material on modernising existing systems.
Legacy Assessment
Understanding what a system does before deciding what to do with it.
The Six Rs
Rehost, replatform, refactor, repurchase, retire, retain — per application.
Rehosting
Lift and shift: fastest, cheapest, and capturing none of the benefits.
Replatforming
Targeted changes that capture operational wins without a rewrite.
Refactoring & Re-architecting
Changing structure incrementally while the system keeps running.
Rebuild vs Re-architect
Why greenfield replacement fails, and the narrow cases where it does not.
Strangler Fig
Routing capabilities to new implementations behind a facade, one at a time.
Application Decomposition
Finding seams in a monolith, starting from the data.
Database Migration
Moving engines, versions and schemas without losing data or uptime.
Zero-Downtime Migration
Expand, migrate, contract — and the contract phase that never happens.
Parallel Run
Shadowing the old system to discover the rules nobody documented.
Cutover Planning
Rehearsals, go/no-go criteria and a rollback that has been executed.
Legacy Integration Patterns
Anti-corruption layers, adapters and CDC against systems that cannot change.
Mainframe Modernization
Batch windows, COBOL, and the risk profile of core banking systems.
Migration Risk
Bounding blast radius, staging by cohort, and honest readiness reporting.
Modernisation Business Case
Pricing tail risk so deferred maintenance becomes fundable.
Coexistence Patterns
Running old and new together for years without corrupting either.
Decommissioning
Actually switching the old system off, and proving nothing depended on it.