Data Transmission Service (DTS) provides an incremental data migration phase that allows you to perform a minimized-downtime migration. You do not have to suspend write requests to the source database during migration. The migration task captures ongoing changes that occur during the full data migration and reapplies the changes after the full data migration is complete.

Prerequisites

  • The version of the user-created SQL Server database is 2008, 2008 R2, 2012, 2014, 2016, or 2017.
    Note
    • SQL Server Cluster or SQL Server AlwaysOn High Availability Group is not supported.
    • If you migrate data between different versions of databases, make sure that the database versions are compatible.
  • The tables to be migrated from the user-created SQL Server database must have primary keys or UNIQUE NOT NULL indexes.
  • The available storage space of the ApsaraDB RDS for SQL Server instance is larger than the total size of the data in the user-created SQL Server database.

Precautions

  • DTS uses read and write resources of the source and destination databases during full data migration. This may increase the database load. If the database performance is unfavorable, the specification is low, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. For example, you can migrate data when the CPU usage of the source and destination databases is less than 30%.
  • To ensure that the incremental data migration task runs as expected, do not frequently back up the source database. We recommend that you retain log files for more than three days. Otherwise, you cannot retrieve log files after they are truncated.
  • To ensure that the delay time of incremental data migration is accurate, DTS adds a heartbeat table to the user-created SQL Server database. The name of the heartbeat table is Source table name_dts_mysql_heartbeat.
  • DTS automatically creates a destination database in the ApsaraDB RDS for SQL Server instance. However, if the name of the source database is invalid, you must create a database in the ApsaraDB RDS for SQL Server instance before you configure the data migration task.
    Note For more information about how to create a database and the database naming conventions, see Create a database for an RDS SQL Server instance.
  • If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.

Limits

  • DTS does not migrate the schemas of assemblies, service brokers, full-text indexes, full-text catalogs, distributed schemas, distributed functions, CLR stored procedures, CLR scalar-valued functions, CLR table-valued functions, internal tables, systems, and aggregate functions.
  • DTS does not migrate data of the sql_variant type.
  • DTS does not migrate tables that contain computed columns.
  • A single data migration task can migrate incremental data from only one database. To migrate incremental data from multiple databases, you must create a data migration task for each database.

Migration types

  • Schema migration

    DTS migrates the schemas of the required objects to the destination instance. DTS supports schema migration for the following types of objects: table, view, trigger, synonym, SQL stored procedure, SQL function, plan guide, user-defined type, rule, and default.

  • Full data migration

    DTS migrates historical data of the required objects from the user-created SQL Server database to the destination ApsaraDB RDS for SQL Server instance.

  • Incremental data migration

    After full data migration is complete, DTS synchronizes incremental data from the user-created SQL Server database to the destination ApsaraDB RDS for SQL Server instance. Incremental data migration allows you to ensure service continuity when you migrate data from a user-created SQL Server database to Alibaba Cloud.

SQL operations that can be synchronized during incremental data migration

  • INSERT, UPDATE, and DELETE
    Note The UPDATE operations that update only the large fields cannot be synchronized.
  • CREATE TABLE
    Note The CREATE TABLE operations used to create partition tables or tables that contain functions cannot be synchronized.
  • ALTER TABLE operations, only including ADD COLUMN, DROP COLUMN, and RENAME COLUMN
  • DROP TABLE
  • RENAME TABLE, TRUNCATE TABLE, and CREATE INDEX

Billing

Migration type Instance configurations Internet traffic
Schema migration and full data migration Free of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Pricing.
Incremental data migration Charged. For more information, see Pricing.

Permissions required for database accounts

Database Schema migration Full data migration Incremental data migration
User-created SQL Server database The SELECT permission The SELECT permission The sysadmin permission
ApsaraDB RDS for SQL Server instance The read/write permissions The read/write permissions The read/write permissions

For information about how to create and authorize a database account, see the following topics:

Incremental data migration

To avoid data migration failures caused by dependencies between objects, DTS migrates the schemas and data of the source SQL Server database in the following order:

  1. Migrate the schemas of tables, views, synonyms, user-defined types, rules, defaults, and plan guides.
  2. Perform full data migration.
  3. Migrate the schemas of SQL stored procedures, SQL functions, triggers, and foreign keys.
  4. Perform incremental data migration.
    Note During schema migration and full data migration, do not perform DDL operations on the objects to be migrated. Otherwise, the objects may fail to be migrated.

Before you begin

Before you configure a data migration task, configure log settings on the user-created SQL Server database.

  1. Run the following command in the user-created SQL Server database to change the recovery mode to full:
    use master;
    GO
    ALTER DATABASE <database_name> SET RECOVERY FULL WITH ROLLBACK IMMEDIATE;
    GO

    Parameters

    <database_name>: the name of the source database.

    Example

    use master;
    GO
    ALTER DATABASE mytestdata SET RECOVERY FULL WITH ROLLBACK IMMEDIATE;
    GO
  2. Run the following command to create a logical backup for the source database. Skip this step if you have already created a logical backup.
    BACKUP DATABASE <database_name> TO DISK='<physical_backup_device_name>';
    GO

    Parameters

    • <database_name>: the name of the source database.
    • <physical_backup_device_name>: the storage path and file name of the backup file.

    Example

    BACKUP DATABASE mytestdata TO DISK='D:\backup\dbdata.bak';
    GO
  3. Run the following command to back up the log entries of the source database:
    BACKUP LOG <database_name> to DISK='<physical_backup_device_name>' WITH init;
    GO

    Parameters

    • <database_name>: the name of the source database.
    • <physical_backup_device_name>: the storage path and file name of the backup file.

    Example

    BACKUP LOG mytestdata TO DISK='D:\backup\dblog.bak' WITH init;
    GO

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. At the top of the Migration Tasks page, select the region where the destination RDS instance resides.Select a region
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure the source and destination databases for the data migration task. Configure the source and destination databases
    Section Parameter Description
    N/A Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select an instance type based on where the source database is deployed. In this example, select User-Created Database with Public IP Address.
    Note If you select other instance types, you must prepare the environments that are required for the source database. For more information, see Preparation overview.
    Instance Region If the instance type is set to User-Created Database with Public IP Address, you do not need to specify the instance region.
    Note If a whitelist is configured for the user-created SQL Server database, you must add the CIDR blocks of DTS servers to the whitelist of the database. You can click Get IP Address Segment of DTS next to Instance Region to obtain the CIDR blocks of DTS servers.
    Database Type Select SQL Server.
    Hostname or IP Address Enter the endpoint that is used to connect to the user-created SQL Server database. In this example, enter the public IP address.
    Port Number Enter the service port number of the user-created SQL Server database. The default port number is 1433.
    Note The service port of the user-created SQL Server database must be accessible over the Internet.
    Database Account Enter the account of the user-created SQL Server database.
    Database Password Enter the password of the source database account.
    Note After you specify the source database parameters, click Test Connectivity next to Database Password to verify whether the specified parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the source database parameters based on the check results.
    Destination Database Instance Type Select RDS Instance.
    Instance Region Select the region where the destination RDS instance resides.
    RDS Instance ID Select the ID of the destination RDS instance.
    Database Account Enter the database account of the destination RDS instance.
    Database Password Enter the password of the destination database account.
    Note After you specify the destination database parameters, click Test Connectivity next to Database Password to verify whether the parameters are valid. If the specified parameters are valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Modify the destination database parameters based on the check results.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to the whitelist of the destination RDS instance. This ensures that DTS servers can connect to the destination RDS instance.
  7. Select the migration types and objects to be migrated. Select the migration types and objects to be migrated
    Parameter Description
    Migration Types
    • To perform only full data migration, select Schema Migration and Full Data Migration.
    • To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. In this example, select all of the three migration types.
    Note If Incremental Data Migration is not selected, do not write data to the user-created SQL Server database during full data migration. This ensures data consistency between the source and destination databases.
    Objects

    Select objects from the Available section and click the Right arrow icon to move the objects to the Selected section.

    Note
    • A single data migration task can migrate incremental data from only one database. To migrate incremental data from multiple databases, you must create a data migration task for each database.
    • You can select columns, tables, or databases as the objects to be migrated.
    • After an object is migrated to the destination database, the name of the object remains unchanged. You can change the names of the objects that are migrated to the destination database by using the object name mapping feature. For more information about how to use this feature, see Object name mapping.
    • If you use the object name mapping feature on an object, other objects that are dependent on the object may fail to be migrated.
  8. In the lower-right corner of the page, click Precheck.
    Note
    • Before you can start the data migration task, a precheck is performed. You can start the data migration task only after the task passes the precheck.
    • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details. Troubleshoot the issues based on the causes and run the precheck again.
  9. After the task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, specify the Channel Specification and select the Data Transmission Service (Pay-As-You-Go) Service Terms.
  11. Click Buy and Start to start the migration task.
    • Full data migration

      Do not manually stop a task during full data migration. Otherwise, data migrated to the destination database will be incomplete. Wait until the migration task automatically stops.

    • Incremental data migration

      An incremental data migration task does not automatically stop. You must manually stop the migration task.

      Note Select an appropriate time to manually stop the migration task. For example, you can stop the migration task during off-peak hours or before you switch your workloads to the destination instance.
      1. Wait until Incremental Data Migration and The migration task is not delayed appear in the progress bar of the migration task. Then, stop writing data to the source database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
      2. After the status of incremental data migration changes to The migration task is not delayed, manually stop the migration task.The migration task is not delayed
  12. Switch your workloads to the destination RDS instance.

What to do next

The database accounts used for data migration have the read/write permissions. After data migration is complete, you must delete the accounts of both the user-created SQL Server database and the ApsaraDB RDS for SQL Server instance to ensure database security.