Database Autonomy Service (DAS) monitors your ApsaraDB RDS for SQL Server instance and automatically expands storage when free space runs low, keeping your workloads running without manual intervention.
For other database engines, see:
Prerequisites
Before you begin, ensure that you have:
An RDS instance that uses cloud disks and runs High-availability Edition or Cluster Edition
A sufficient Alibaba Cloud account balance to cover the cost of additional storage
The AliyunServiceRoleForDAS service-linked role (if it does not exist, DAS creates it automatically before the first expansion)
How it works
When free storage on the primary instance drops to or below the threshold you set, DAS triggers an expansion. The expansion size is the larger of:
5 GB — or 10 GB if total storage is less than 50 GB and free space is below 10% of capacity
15% of current storage capacity, rounded to the nearest multiple of 5 GB
For example, a 100 GB instance expands by 15 GB (15% of 100 GB) and reaches 115 GB after expansion.
DAS waits at least 10 minutes between consecutive expansions.
If the instance has read-only instances attached, DAS checks each read-only instance before expanding the primary:
DAS identifies any read-only instance whose storage would fall below the primary's post-expansion size.
DAS expands those read-only instances first.
Once all read-only instances meet the requirement, DAS expands the primary instance.
Limitations
Automatic storage expansion is not available for some SQL Server instances due to Windows driver restrictions. To resolve this, update the minor engine version.
Automatic storage expansion cannot be configured separately for read-only instances.
DAS does not expand storage if doing so would exceed the Maximum storage of automatic expansion value you configure.
Billing
Automatic storage expansion is billed the same way as manual storage expansion. For details, see Specification changes.
Enable automatic storage expansion
Log on to the DAS console.
In the left-side navigation pane, choose Intelligent O&M Center > Instance Monitoring.
Find the instance you want to manage and click its ID to open the instance details page.
In the left-side navigation pane, click Autonomy Center.
In the upper-right corner, click Autonomy Service Settings.
On the Autonomous Function Settings tab of the Autonomous Function Management panel, enable the automatic storage expansion feature.
On the Optimization and Throttling tab, select Automatic Space Expansion and configure the following parameters.
Parameter Description Available Storage Space ≤ The threshold that triggers expansion. When free storage drops to or below this value, DAS expands the instance. Maximum Storage of Automatic Expansion The upper limit on storage capacity after expansion. Set this to at least the current storage capacity. We recommend setting it significantly higher than the current capacity to handle expected growth and avoid hitting the ceiling before you can adjust it. DAS does not expand storage beyond the Maximum Storage of Automatic Expansion value, even if the threshold is reached. Set this value high enough to handle your expected growth.
Click OK.
(Optional) In the Alert Configuration section, configure an alert template to receive notifications about expansion events. The system recommends an alert template and adds the required alert rules automatically. Follow the on-screen prompts to complete the setup.
If you already have an alert template for this instance, add the required alert rules for autonomy events to the existing template as prompted.
If you need to create an alert template from scratch, see Configure alert templates and Configure alert rules. To configure alert contacts:
In the Select Alert Contact Group step, select an alert contact group. For more information, see Manage alert contacts.
Click Add Contact to add a new alert contact.
Click Create Contact Group to create a new alert contact group.
Click Edit or Remove in the Actions column to modify or delete an existing contact.
In the Associate with Resources step, confirm the associated resources.
Click Submit Configuration and confirm in the dialog box that appears.
View expansion results
Log on to the DAS console.
In the left-side navigation pane, choose Intelligent O&M Center > Instance Monitoring.
Find the instance and click its ID to open the instance details page.
In the left-side navigation pane, click Autonomy Center.
Select a time range to filter Auto-Scaling Events.
Click Details to view the results of a specific expansion event.
What's next
Auto Scaling overview — Learn how DAS auto scaling works across storage and other dimensions.
AliyunServiceRoleForDAS role — Understand the permissions DAS uses to manage your instances.