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    Data Transmission Service:Create a reverse instance

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    Data Transmission Service:Create a reverse instance

    Last Updated:Mar 28, 2026

    After you switch workloads from the source database to the destination database, new writes accumulate in the destination database and need to flow back to the source database before you can safely fail back. A reverse instance in Data Transmission Service (DTS) synchronizes this incremental data from the destination back to the source, enabling a controlled failback. This feature is often used for database disaster recovery.

    How it works

    A reverse instance runs in the opposite direction of your original synchronization instance: it reads incremental data written to the destination database and applies it to the source database.

    The failback workflow follows three sequential steps:

    1. Create the reverse instance — DTS immediately runs a precheck. After the precheck passes, DTS starts collecting incremental data from the destination database but does not write it to the source database until the reverse instance is started.

    2. Pause the forward synchronization instance — prevents data conflicts between the two directions.

    3. Start the reverse instance — DTS begins writing the collected incremental data to the source database.

    Important

    Pause the forward synchronization instance before starting the reverse instance. Starting both at the same time can cause data inconsistency or instance failure.

    Prerequisites

    Before you begin, ensure that you have:

    • An original data synchronization instance that is running with incremental data synchronization in progress, where the source and destination databases are SQL Server, MySQL, or ApsaraDB for MongoDB

    • The required permissions granted to the destination database account of the original synchronization instance:

      • SQL Server: The sysadmin role. Run the following command using a system administrator account to grant the role: EXEC sp_addsrvrolemember @loginame = N'<Account name>', @rolename = N'sysadmin';

      • MySQL: The REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT permissions. For details, see GRANT Statement.

      • ApsaraDB for MongoDB: Read permissions on the source database, the admin database, and the local database. For details, see Use DMS to manage database accounts.

    Limitations

    • Supported database types: SQL Server, MySQL, and ApsaraDB for MongoDB.

      Important

      If the original instance is a data synchronization instance between SQL Server databases or between MySQL databases, this feature is available only for the destination ApsaraDB databases.

    • Synchronization type: Only Incremental Data Synchronization is supported for the Synchronization Types parameter.

    • Pre-creation writes are not synchronized: Data written directly to the destination database before the reverse instance is created is not synchronized.

    • One reverse instance per synchronization instance: After the reverse instance is started, the original synchronization instance cannot be started directly.

    • Cross-border instances are not supported.

    Create a reverse instance

    Step 1: Create the reverse task

    1. Go to the Data Synchronization Tasks page.

      • DTS console: Log on to the DTS console. In the left-side navigation pane, click Data Synchronization, then select the region in the upper-left corner.

      • Data Management Service (DMS) console: Log on to the DMS console. In the top navigation bar, move the pointer over Data Development and choose DTS (DTS) > Data Synchronization. Select the region from the drop-down list to the right of Data Synchronization Tasks.

        Note

        The actual steps may vary depending on the mode and layout of the DMS console. For details, see Simple mode and Customize the layout and style of the DMS console.

    2. Find the data synchronization instance.

    3. In the Actions column, click the 更多设置 icon and select Create Reverse Task.

    4. In the Note dialog, click OK. Wait until the precheck completes and the Status column shows Performing Initial Synchronization.

      Note

      • If Auto Refresh is disabled, click the Refresh icon to refresh the status.

      • If the precheck fails, click View Cause, then click View Details in the Check Result column of the failed item. Follow the instructions to fix the issue and run the precheck again.

    Step 2: Pause the forward synchronization instance

    Pause the original instance before starting the reverse instance to prevent data conflicts.

    1. On the Data Synchronization Tasks page, find the original synchronization instance.

    2. In the Actions column, click the 更多设置 icon and select Pause Task.

    3. In the Note dialog, click OK.

    4. In the The task is paused. dialog, click OK.

    Step 3: Start the reverse instance

    1. On the Data Synchronization Tasks page, click the ID of the reverse instance.

    2. In the Actions column, click the 更多设置 icon and select Start Reverse Task.

    3. In the Note dialog, click OK.

    DTS begins writing incremental data from the destination database to the source database.

    FAQ

    Can I create a reverse instance for a migration instance?

    No. Reverse instances are supported only for data synchronization instances between SQL Server, MySQL, or ApsaraDB for MongoDB databases. Migration instances are not supported.

    What do I do if the Data Backups item fails the precheck of the reverse instance?

    Enable log backup in the source database and run the precheck again.

    • Self-managed SQL Server: Click View Details in the Check Result column to see the required backup method.

    • ApsaraDB RDS for SQL Server: Manually back up the database. See the Configure manual backups section of the backup topic.

    What's next

    For background on the reverse task feature and its use in disaster recovery scenarios, see Create a reverse task.