## TL;DR

Set a CloudWatch alarm on FreeStorageSpace well before it matters, and remember RDS storage only grows, never shrinks, with a cooldown of roughly 6 hours between scaling events.

## Steps

1. Do not trust a set MaxAllocatedStorage value alone; confirm MaxAllocatedStorage is greater than AllocatedStorage or autoscaling is effectively off. Set a CloudWatch alarm on FreeStorageSpace well before it matters, and remember RDS storage only grows, never shrinks, with a cooldown of roughly 6 hours between scaling events.

## When to use

You are seeing this: Autoscaling only kicks in when MaxAllocatedStorage is greater than AllocatedStorage; if they are equal, RDS cannot grow and a full disk takes the instance down. Use this skill when you run into "RDS storage autoscaling needs MaxAllocatedStorage above AllocatedStorage".

## When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

## Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

## Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.