ITPEC FE Morning October 2021 Question 56

It must set the criteria for deciding to return to the old system if the migration fails — a migration plan needs a fallback, with the decision rule fixed in advance.

A migration plan covers the method (all at once, parallel, phased or pilot), the schedule, data migration, the checks that confirm success, and a contingency: the point and the criteria at which the switchover is abandoned and the old system restored. Fixing these beforehand avoids an improvised judgement under time pressure.

Answer (a)

Why not others:

• •(b) — running both systems in parallel doubles operation and data entry, so it raises cost; what it lowers is risk.
• •(c) — a shared environment ties the systems together, so a problem in one affects the other and results are hard to attribute to either; separate environments make the migration status easier to verify.
• •(d) — the more data there is, the longer a single batch takes and the more a failure costs right before the switch; large volumes are migrated in advance or in stages, leaving only the changes for the switchover.

Key rule: Plan the failure path as carefully as the success path: a migration plan fixes in advance when and how to fall back to the old system.

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