Database Autonomy Service (DAS) monitors storage usage on your ApsaraDB RDS for PostgreSQL instance and expands storage capacity automatically when usage reaches a threshold you define. This keeps your database running without manual intervention and prevents storage-full outages.
For other database engines, see the following topics:
ApsaraDB RDS for MySQL: Use the automatic storage expansion feature
ApsaraDB RDS for SQL Server: Configure automatic storage expansion
Prerequisites
Before you begin, ensure that you have:
An RDS instance that uses cloud disks
A sufficient Alibaba Cloud account balance to cover the expansion cost (billed the same as manual storage expansion; see Specification changes)
A service-linked role for DAS — the system creates the AliyunServiceRoleForDAS role automatically if it does not exist
How automatic storage expansion works
When storage usage reaches the configured threshold, the system expands capacity automatically.
Trigger conditions: The system initiates expansion when all of the following are true:
Used storage space reaches or exceeds the threshold you set (50%–90% of total capacity)
At least 10 minutes have passed since the last expansion
Expansion size: The system adds whichever is larger:
5 GB
15% of current storage capacity, rounded to the nearest multiple of 5
Example: Current storage is 100 GB. 15% equals 15 GB, which is larger than 5 GB. The system adds 15 GB, bringing total storage to 115 GB.
Special case: If the instance has less than 50 GB of storage and available storage is below 10% of total capacity, the minimum expansion step is 10 GB instead of 5 GB.
Read-only instance handling: If your primary instance has read-only instances, the system checks each read-only instance first. If a read-only instance has less storage than the primary instance will need after expansion, the system expands the read-only instances before expanding the primary instance.
Backup in progress: If the instance is being backed up when the threshold is reached, the expansion task starts after the backup completes.
Limitations
Storage cannot be reduced automatically. After an expansion, reduce storage manually by changing instance specifications. See Change instance specifications.
Maximum storage limits: 32,000 GB for Enhanced SSDs (ESSDs), 6,000 GB for standard SSDs.
Configure automatic storage expansion
Step 1: Open the instance
Go to the Instances page. In the top navigation bar, select the region where your RDS instance resides, then click the instance ID.
Step 2: Open Autonomous Function Management
In the left-side navigation pane, use either path:
Choose Autonomy Services > Diagnostics. On the page that appears, click the Autonomy Center tab, then click Autonomy Service Settings.
Choose Autonomy Services > Dashboard, then click Autonomy Service Settings.
Step 3: Add a policy
On the Autonomous Function Settings tab, click Auto Scaling, then click Add Policy.
In the panel that appears, configure the following parameters.
Parameter Description Policy Name A name for the policy. Mode Select Automatic Storage Expansion. Engine Type Only RDS PostgreSQL is supported. Specifications Only Disks is supported. Used Storage Space >= The storage usage percentage that triggers expansion. Valid values: 50%–90%. Default: 50%. Maximum Storage The upper limit for storage capacity after automatic expansion. Must be greater than or equal to the current total storage. Maximum values: 32,000 GB for ESSDs, 6,000 GB for standard SSDs. Click OK.
Step 4: Apply the policy
In the Recommended Policies section, click Apply in the Actions column.
To modify a policy later, click the entry in the Modify column, then update the settings in the Update Policy panel. To remove a policy from the instance, find it in the Applied Policies section and click Cancel.
View expansion results
Go to the Autonomy Center page and select a time range.
In the Elastic Scaling Events section, click Details to view the results of each expansion.
