A non-Aurora RDS for MySQL DB instance has 200 GiB allocated and storage autoscaling disabled. Warn operators when free storage falls below 20 GiB.
Evaluate the selected DBInstanceIdentifier every minute and notify a prepared SNS topic after three consecutive periods below 20 GiB.
Which metric should be compared with a threshold in bytes?
Compare FreeStorageSpace Bytes with the converted 20 GiB threshold and configure evaluation and SNS notification.
Detailed explanation
It measures available storage in Bytes and supports the converted 20 GiB threshold.
It measures available storage in Bytes and supports the converted 20 GiB threshold.
I/O rates measure activity, not remaining disk bytes.
I/O rates measure activity, not remaining disk bytes.
Connection count cannot replace free-space measurement; few connections can still exhaust storage.
Connection count cannot replace free-space measurement; few connections can still exhaust storage.
FreeableMemory measures available RAM, not free database storage.
FreeableMemory measures available RAM, not free database storage.
Check official documentation
Compare the following points with the official documentation.
Compare FreeStorageSpace/FreeableMemory definitions and units and review autoscaling conditions and limits.
Official references
What to confirm
Convert 20 GiB to 21,474,836,480 bytes and distinguish a warning from capacity expansion.
Key points
- FreeStorageSpace
- RDS
- Storage exhaustion
Notes
- Environment: AWS SOA-C03 exam guide and the linked AWS documentation
- Reviewed against the linked AWS documentation on 2026-10-04.
Foundation review
Align units, resources, and evaluation
20 GiB is 21,474,836,480 bytes, not a threshold of 20 bytes. Select the DB dimensions; for example, use one-minute Minimum with EvaluationPeriods=3 and DatapointsToAlarm=3, a below-threshold condition, and SNS. Decide how missing data is handled; it is not evidence of sufficient free space.
Connect warning to a capacity response
An alarm does not expand storage. Investigate retention and growth, then plan safe cleanup and expansion. With autoscaling, check the maximum, optimization restrictions, and headroom for rapid growth. Autoscaling alone cannot completely prevent storage-full conditions.