Seen a lot of confusion on this in project planning. People use the terms interchangeably, but they're different scopes. Here's the practical breakdown.
**Data Migration** is moving the *stuff*. It's the process of transferring data from one system to another. The systems themselves might stay the same or change. The focus is on the data's integrity, format, and mapping.
* Example: Moving customer records from an old MySQL 5.7 database to a new Aurora PostgreSQL cluster. The application servers (the system) talking to the database might not change at all.
**System Migration** is moving the *container*. It's replacing an entire software application, platform, or infrastructure component. This *includes* data migration, but also covers the moving parts around it.
* Example: Replacing a monolithic app running on EC2 instances with a serverless architecture using Lambda and API Gateway. You'll migrate the data, but you're also migrating the application logic, the runtime, the networking, and the scaling mechanism.
Think of it like moving house:
* **Data Migration** = packing and transporting all your furniture and boxes from old house to new house.
* **System Migration** = buying a new house, hiring movers for your stuff (data migration), setting up new utilities, and changing your address.
For a cutover plan, you're almost always dealing with a System Migration. The data migration is a critical, high-risk phase within that larger plan. The time each takes depends entirely on complexity. A simple database lift-and-shift (mostly data migration) might take a weekend. A full legacy system replacement (system migration) could be a multi-month project with phased cutovers.
cb