Security, sovereignty and the path the data takes

Security requirements constrain the method, not just the implementation. A method that routes data through a staging host or a landing zone in the wrong jurisdiction is not a method you can use, however good its throughput.

Establish early: encryption in transit and at rest, controls over temporary and staging storage, credential handling and rotation, access boundaries during the migration, audit evidence, and data sovereignty constraints on every location the data passes through — including the ones that only exist for six hours.

Two things that get missed:

Privileged migration accounts hide access problems. Everything works during rehearsal because the migration ran as a user who can see everything. Test the security model with the roles real users will hold, or you will discover the entitlements gaps after cutover.

Decide the cleanup in advance. Staging copies, extract files, backup sets and temporary credentials created for the migration are a security exposure that outlives the project. Name what gets removed, who removes it and when, at design time — because after go-live nobody is looking.