RDS Instance not triggering an storage auto-scaling event.

Question

I have an RDS Instance running SQL Server SE 14.00.3381.3.v1 Multi-AZ. The instance has autoscaling enabled with the upper threshold set at 4500GB, 
I have been getting database event notifications stating the free space is less than 10% for the last two days
```
The free storage capacity for DB Instance: databaseName is low at 10% of the provisioned storage [Provisioned Storage: 3848.87 GB, Free Storage: 385.30 GB]. You may want to increase the provisioned storage to address this issue.
```
Now my question is when does the scaling event trigger? I thought this might be done during the maintenance window, but the maintenance window was today morning and the storage auto-scaling was not triggered.
I did update the Autoscaling threshold today morning to 5000GB to see if this solved the issue, but no storage scaling so far.

The autoscaling of storage has worked previously, so not sure why the storage is not getting scaled up this time. is there anything in the RDS logs I should look for?

Thanks
Sanoob

Answer

Dear Customer,

Thanks for reaching out to us via AWS re:Post.

AWS storage auto-scaling for RDS gets triggered based off the below conditions->

With storage autoscaling enabled, when Amazon RDS detects that you are running out of free database space it automatically scales up your storage. Amazon RDS starts a storage modification for an autoscaling-enabled DB instance when these factors apply:
>Free available space is less than 10 percent of the allocated storage.
>The low-storage condition lasts at least five minutes.
>At least six hours have passed since the last storage modification, or storage optimization has completed on the instance, whichever is longer.

The additional storage is in increments of whichever of the following is greater:
>5 GiB
>10 percent of currently allocated storage
>Storage growth prediction for 7 hours based on the FreeStorageSpace metrics change in the past hour. For more information on metrics, see Monitoring with Amazon CloudWatch

[] Working with storage for Amazon RDS DB instances - Managing capacity automatically with Amazon RDS storage autoscaling - https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_PIOPS.StorageTypes.html#USER_PIOPS.Autoscaling

Auto-scaling does not exclusively wait for the maintenance window.

Hope I was able to shed some light on the matter for you - Have a great rest of the day!

RDS Instance not triggering an storage auto-scaling event.

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