Forum Discussion
SQL Server Mirroring keeps giving error when I want to add more tables
Hi sholy29
Thank you for the detailed update and the screenshot.The error message “Test connection failed. The Data Factory runtime is busy now. Please retry the operation later” shows that the issue is now due to a runtime resource contention in Microsoft Fabric’s backend, specifically the Data Factory runtime that manages mirroring and data movement. This usually happens when there are many concurrent operations, like active mirroring or data transformation jobs, which can temporarily use up available resources.
To address this, it’s recommended to wait 15–30 minutes and then try again, as these issues often resolve themselves. Also, try to avoid running overlapping workloads at the same time pause any active pipelines, Dataflows, or Power BI dataset refreshes if possible.
Additionally, If you have access, use a dedicated Fabric capacity workspace, since lower SKUs or trial capacities are more likely to encounter this issue. You might also try using a new browser session or incognito window to prevent session token problems. For authentication, using a linked service with a stored SQL username and password is valid for mirroring, so no changes are needed there.
Thank you for being part of Fabric Community Forum.
Regards,
Karpurapu D,
Microsoft Fabric Community Support Team.
Community SupportHi sholy29
Welcome to the Microsoft Fabric Community Forum.
The error encountered when attempting to add more tables to an existing SQL Server mirroring setup in Microsoft Fabric, specifically “Test connection failed. Request failed with status code 400,” is typically caused by transient backend service issues, gateway misconfigurations, unsupported schema elements, or disabled tenant settings. While previously mirrored tables continue to function, new additions may trigger revalidation processes that expose these underlying issues.
To resolve this, retry the operation after a short delay, as transient errors often self-resolve. Additionally, ensure the on-premises data gateway is properly configured and restarted, and that SQL authentication is used for connectivity. Review the schema of the new tables to confirm they do not contain deprecated data types such as TEXT, NTEXT, or IMAGE.
In the Microsoft Fabric Admin Portal, verify that the tenant setting “Users can access data stored in OneLake with apps external to Fabric” is enabled. If previous mirroring attempts left residual metadata, use SQL commands such as sp_change_feed_drop_table_group to clean up stale entries. Finally, add tables incrementally and monitor replication status using diagnostic views like sys.dm_change_feed_errors to isolate and address specific issues. These steps have been validated across multiple incident reports and align with Microsoft’s recommended practices for ensuring reliable mirroring to Fabric.
Regards,
Karpurapu D,
Microsoft Fabric Community Support Team.