Moving off the old system,
one verified, reversible batch at a time
Migrating off a legacy system is where businesses lose real data, not from carelessness but from doing it all at once and discovering a mismatch after it is too late to easily undo. A legacy migration agent maps the old schema to the new one, writes the transform scripts, and moves data in small batches, each one backed up first and checksum-verified after, so a problem shows up in batch three instead of after everything has already moved.
The role today
A legacy system migration usually gets attempted once, under time pressure, as close to “all at once” as the team can manage, because breaking it into careful stages feels slower than the deadline allows. That is exactly the setup where a mismatched field or a silent data loss only surfaces weeks later, after the old system has already been decommissioned and there is nothing left to check against.
The second cost is that mapping the old schema to the new one by hand is slow and error-prone precisely where it matters most: the edge cases, the field that means something slightly different in each system, the record format nobody fully remembers the rules for anymore.
The third is that a failed migration rarely fails loudly. It fails quietly, a few hundred records out of tens of thousands landing wrong, and that kind of error is much harder to catch after the fact than before.
What the agent takes over
The agent maps the old system’s schema to the new one, field by field, flags ambiguous cases for a human instead of guessing, and writes the transform scripts. It runs the migration in small batches rather than one pass, backing up the source before every batch and checksum-verifying the result against it afterward, row counts, totals, key fields matching exactly.
If a batch does not verify, it stops there and a named rollback command undoes just that batch, so a problem in batch twelve does not threaten batches one through eleven that already checked out clean. A reconciliation report at the end compares old and new side by side, the same discipline we used recovering 571 of 571 orders from a raw chat history and matching it to the bank down to the figure.
Typical scope: moving data between a legacy and a new system, reconciling totals, and keeping the old system intact as a reference until the new one is proven.
What stays with humans
Approving the cutover window - when the old system stops being the source of truth - is a human decision, not an automatic switch. Edge cases the mapping cannot resolve on its own get escalated rather than guessed at. Final sign-off that the migration is complete and the old system can be retired stays with your team.
Guards
Every batch is backed up before it runs and checksum-verified after. A failed verification stops that batch with a named, tested rollback command, not a manual scramble. The migration always runs in reversible batches, never as one irreversible pass. The old system is never deleted or altered until the full migration is verified and approved.
Price and timeline
| Option | Price | What it covers | Timeline |
|---|---|---|---|
| Agency runs it | from $3,500 + support plan | Migration built, run and verified by us, supervised cutover window | 3 to 6 weeks |
| Full control, handover-ready | from $5,900 | Same migration on your own infrastructure, documented mapping and scripts, your team owns the cutover | 5 to 8 weeks |
Running cost during migration is usually $20 to $60 a month in compute; there is no ongoing cost once the cutover is complete.
Related
See the AI agents service page and development for the surrounding build. Within this group: data quality agent, backup and recovery agent, and data engineering and ETL agent cover adjacent ground before and after a migration. For one-time project versions, see automate data migration between systems and automate database migration safety checks. Real recovery work behind this page: the sports nutrition sales case study, where 571 of 571 orders were recovered from a chat history, and the ProBay AI agent team case study.
Dreading the cutover off an old system? Get in touch and we will map what actually needs to move first.
FAQ
How much does a legacy migration agent cost?
From $3,500 for a single system migration with a clear source and target, live in 3 to 6 weeks. A more complex migration with multiple sources or unclear legacy data usually runs $5,000 to $9,000.
How long does the actual cutover take?
3 to 6 weeks total, most of it mapping and testing against real data. The live cutover itself happens in batches over a window you approve, often a few days to two weeks depending on data volume.
Which systems can it migrate between?
Any two systems with inspectable data, databases, exports, APIs, or even a chat history, as we did recovering 571 of 571 orders from a Telegram channel. It does not need a clean API on either side to work.
What if a batch does not match after migrating?
It stops there. Every batch is checksum-verified against the source before moving to the next, and a named rollback command undoes a failed batch without touching the ones that already verified correctly.
Is our data ever at risk during this?
The old system stays untouched and readable throughout, migration only ever writes to the new system, and a full backup exists before every single batch. Nothing is deleted from the source until the whole migration is verified and you have signed off.