## TL;DR
Automated backups obey the retention window, but manual snapshots and snapshots copied across regions or accounts do not; they accumulate forever. List all snapshots for the instance, delete the ones you no longer need, and watch the backup storage billing fall.

## Use this when
- RDS backup storage grows month over month.
- The retention window is set (say 7 days) but storage keeps climbing.
- The bill shows backup storage far above the DB size.

## Not for this skill when
- You want to change the retention window itself. That is a parameter change.
- Backups are failing. That is an operational problem.

## Steps
1. List automated backups versus manual snapshots for the instance. Verify: you can separate the two lists.
2. Check for snapshots copied to other regions or shared with other accounts; copies are independent objects. Verify: you have the full inventory including copies.
3. Identify deletion candidates: old manual snapshots superseded by newer ones, pre-migration snapshots kept just in case, copies of deleted instances. Verify: each candidate has a documented reason to go or a newer replacement.
4. Delete the candidates. Verify: the snapshot list shrinks.
5. Watch the backup storage metric and the next bill. Verify: storage stops growing and then declines.

### Deleted instance variant
Snapshots of deleted instances become manual snapshots that persist. Verify: orphaned snapshots are included in the inventory.

Compatibility: RDS (all engines), Aurora has its own backup model with similar manual-snapshot behavior.

## Why it happens
The retention window only governs automated backups. Every manual snapshot, including ones created by copy operations and ones left behind by deleted instances, is retained until someone deletes it, and each one bills for its full size.

## Edge cases / pitfalls
- Deleting a snapshot is irreversible. Confirm the replacement exists before deleting.
- Final snapshots taken at instance deletion are manual and persist; name them clearly at creation.
- Cross-region copies bill in the destination region at its rates.
- Backup storage beyond the free allowance (one DB-size worth) is what actually bills; small growth under that is free.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_MfcwfDpngEtf_M3aL8qZ5g