RDS Oversized Storage
CostLens flags RDS instances where more than 80% of allocated storage is unused.
CostLens flags RDS instances where more than 80% of allocated storage is unused. You are paying for storage your database doesn't use. This is an informational recommendation only — RDS storage cannot be decreased directly; the account is informed so the team can plan a replacement or migration.
No automated fix available
AWS does not allow RDS storage to be reduced. Once allocated storage is set, it can only grow — never shrink. To reclaim storage, you must create a new RDS instance with the correct storage size, migrate data to it, and decommission the original. CostLens surfaces this as an informational finding so your team can plan the migration.
How it works
CostLens queries FreeStorageSpace
Queries CloudWatch FreeStorageSpace for each RDS instance, averaged over 7 days.
Compares against AllocatedStorage
The free storage is compared against the AllocatedStorage from the RDS API.
Flags instances where 80%+ is free
Instances where free / allocated > 80% and allocated storage is > 20 GB are flagged.
Shows overpayment estimate
The finding shows the allocated size, average free storage, and estimated monthly overpayment.
What to do
Option 1 — Migrate to a smaller instance (recommended)
- Snapshot the current RDS instance.
- Restore the snapshot to a new instance with smaller storage allocation.
- Update application connection strings to point to the new instance.
- Delete the old instance after verifying the new one works correctly.
Option 2 — Enable RDS autoscaling (prevent future overpayment)
Enable storage autoscaling in the RDS console (Modify → Storage → Enable autoscaling with a sensible max). For new instances, start with minimal storage and let autoscaling grow it as needed.
Option 3 — Dismiss if planned for future growth
If the storage was allocated intentionally for anticipated data growth, dismiss the recommendation to prevent it from reappearing.
Severity levels
| Severity | Allocated storage |
|---|---|
| high | >500 GB with >80% free — significant monthly waste |
| medium | 100–500 GB with >80% free |
| low | 20–100 GB with >80% free — minor saving, low priority |
Tip
For new RDS instances, always start with the minimum storage needed and enable Storage Auto Scaling. This avoids over-provisioning while still accommodating growth automatically.