A short guide to data migration

This is one of those topics that looks small until it costs you something. Everything we would tell a client about data migration in the time it takes to drink a coffee.

Numbers get quoted in meetings long after anyone remembers how they were calculated. Write the reasoning down alongside the decision, because the reasoning is what changes first.

Why this earns attention

Migrations fail on the data nobody knew existed. In practice this is a scheduling problem more than a technical one. The teams that stay on top of it are the ones who put it on a calendar rather than a wish list.

The practical version

Run it against a full copy before the real thing. It is worth being explicit about, because assumptions differ quietly. If two people in the business would answer this differently, that gap is the actual problem.

What to watch for

Always have a documented way back. The teams that handle this well are rarely the ones with the biggest budgets. Check it against what you would want a competitor's site to get wrong.

How to tell if yours is fine

Data outlives the applications built on top of it, which is why the model deserves more thought than the screens. Three things worth confirming about data migration before you move on:

• Someone can say what the current setup is without going to look
• Run it against a full copy before the real thing — and you know whether that is true here
• There is a way to tell whether the last change to this helped

If any of that sounds like a description of your current setup, it is fixable.