Two server rooms migrated in one weekend, London

The challenge

Two server rooms, 38 racks of mixed-age hardware, undocumented cabling and a business that could not be offline past Monday 06:00. Legacy equipment had no current spares, and two applications had no tested failover. The client's instinct was a big-bang move; the risk profile said otherwise.

The result

The migration completed at 03:40 on Sunday, twenty hours inside the window. Two applications were reverted to the rollback position when post-move validation failed, then migrated successfully in the second batch — the plan absorbed the failure instead of the business absorbing it. All 412 drives sanitised with per-drive certificates.

“The rollback positions are why we signed. Nobody else put in writing how they would undo it.”