Migrate data between ApsaraDB RDS for SQL Server instances - Data Transmission Service

This topic describes how to migrate data between ApsaraDB RDS for SQL Server instances by using Data Transmission Service (DTS).

Prerequisites

The source and destination ApsaraDB RDS for SQL Server instances are created. For information about the supported database versions, see Overview of data migration scenarios. For information about how to create an ApsaraDB RDS for SQL Server instance, see Create an ApsaraDB RDS for SQL Server instance.
Important
- If the engine version of the source ApsaraDB RDS for SQL Server instance is 2008 or 2008 R2, incremental data migration is not supported.
- If the SQL Server Incremental Synchronization Mode parameter is set to Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables, data is migrated in hybrid log-based parsing mode and you can use one of the following engine versions for the source database:
  - Self-managed SQL Server or ApsaraDB RDS for SQL Server database of the Enterprise or Enterprise Evaluation edition: version 2012, 2014, 2016, 2019, or 2022.
  - Self-managed SQL Server or ApsaraDB RDS for SQL Server database of the Standard edition: version 2016, 2019, or 2022.
The available storage space of the destination ApsaraDB RDS for SQL Server instance is larger than the total size of the data in the source ApsaraDB RDS for SQL Server instance.
Multiple DTS instances are purchased to configure multiple data migration tasks if the source ApsaraDB RDS for SQL Server instance meets one of the following conditions:
- The source instance contains more than 10 databases.
- A single database of the source instance backs up its logs at an interval of less than 1 hour.
- A single database of the source instance executes more than 100 DDL statements each hour.
- Logs are written at a rate of 20 MB/s for a single database of the source instance.
- The change data capture (CDC) feature needs to be enabled for more than 1,000 tables in the source ApsaraDB RDS for SQL Server instance.

Usage notes

Note

DTS does not migrate foreign keys in the source database to the destination database. Therefore, the cascade and delete operations of the source database are not migrated to the destination database.

Limit type	Description
Limits on the source database	The server on which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If you select tables as the objects to be migrated and you need to edit the tables in the destination database, such as renaming tables or columns, you can migrate up to 1,000 tables in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables or configure a task to migrate the entire database. You can run a single data migration task to migrate up to 10 databases. If you want to migrate more than 10 databases, we recommend that you configure multiple tasks to migrate the databases. Otherwise, the performance and stability of your data migration task may be compromised. If you want to migrate incremental data, make sure that the following requirements are met: The data logging feature must be enabled. The backup mode must be set to Full and full physical backup must be performed. If you perform only incremental data migration, the data logs of the source database must be retained for more than 24 hours. If you perform both full data migration and incremental data migration, the data logs of the source database must be retained for at least seven days. Otherwise, Data Transmission Service (DTS) may fail to obtain the data logs and the task may fail. In some cases, data inconsistency or loss may even occur. After full data migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of data logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. If the change data capture (CDC) feature needs to be enabled for the tables that you want to migrate from the source database, the following conditions must be met. Otherwise, the precheck fails. The value of the srvname field in the sys.sysservers view is the same as the return value of the SERVERPROPERTY function. If the source database is a self-managed SQL Server database, the database owner must be the sa user. If the source database is an ApsaraDB RDS for SQL Server database, the database owner must be the sqlsa user. If the source database is of the Enterprise edition, you must use SQL Server 2008 or later. If the source database is of the Standard edition, you must use SQL Server 2016 SP1 or later. If the source database is of the Standard or Enterprise edition and its version is SQL Server 2017, we recommend that you update the version. DTS uses the fn_log function to obtain the logs of the source database. However, this function has performance bottlenecks. We recommend that you do not clear the logs of the source database before the task is complete. Otherwise, the task may fail. Limits on operations on the source database: During schema migration and full data migration, do not execute DDL statements to change the schemas of databases or tables. Otherwise, the data migration task fails. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data will be inconsistent between the source and destination databases. To ensure data consistency, we recommend that you select Schema Migration, Full Data Migration, and Incremental Data Migration as the migration types. If the source database is a read-only instance, you cannot migrate DDL operations. In hybrid log-based parsing mode, you cannot perform multiple operations to add columns to or remove columns from the source database within 10 minutes. For example, if you execute the following SQL statements within 10 minutes, an error is reported for the task. `ALTER TABLE test_table DROP COLUMN Flag; ALTER TABLE test_table ADD Remark nvarchar(50) not null default('');` If the source database is an ApsaraDB RDS for SQL Server instance that runs SQL Server Web edition, you must set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) when you configure the task.
Other limits	DTS does not migrate data of the following types: CURSOR, ROWVERSION, SQL_VARIANT, HIERARCHYID, POLYGON, GEOMETRY, and GEOGRAPHY. If you set the SQL Server Incremental Synchronization Mode parameter to Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported) in the Select Objects step, the tables to be migrated must have clustered indexes that contain primary key columns. The tables to be migrated cannot be heap tables, tables without primary keys, compressed tables, or tables with computed columns. Ignore the preceding limits if the hybrid log-based parsing mode is used. Note For more information about how to view table information, see the How do I view the information about heap tables, tables without primary keys, compressed tables, and tables that contain computed columns in an SQL Server database? section of the FAQ topic. If you set the SQL Server Incremental Synchronization Mode parameter to Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables (Hybrid Log-based Parsing) in the Select Objects step, DTS uses the CDC component to migrate incremental data. Make sure that the CDC job in the source database runs as expected. Otherwise, the DTS task fails. If you set the SQL Server Incremental Synchronization Mode parameter to Polling and querying CDC instances for incremental synchronization in the Select Objects step, the following limits apply: The source database account used by the DTS instance must have the permissions to enable the CDC feature. To enable database-level CDC, you must use an account that is assigned the sysadmin role. To enable table-level CDC, you must use a privileged account. Note A server administrator account in Microsoft Azure SQL Database has the required permissions. CDC can be enabled for all databases that are purchased in Azure SQL Database based on the vCore model. CDC can be enabled for databases that are purchased in Azure SQL Database based on the database transaction unit (DTU) model only if the databases have a service tier of S3 or greater. A privileged account of an Amazon RDS for SQL Server instance has the required permissions. CDC can be enabled for stored procedures at the database level. DTS obtains incremental data by performing round-robin queries on the CDC instance of each table in the source database. Therefore, the number of tables to be migrated from the source database cannot exceed 1,000. Otherwise, the data migration task may be delayed or unstable. You cannot execute a DDL statement to add or remove columns more than twice within a minute. Otherwise, the data migration task may fail. During data migration, you cannot modify the CDC instances of the source database. Otherwise, the data migration task may fail or data loss may occur. If you want to migrate data between different versions of databases, make sure that the database versions are compatible. In Incremental Synchronization Based on Logs of Source Database mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history in the source database to ensure that the latency of data migration is accurate. In hybrid log-based parsing incremental synchronization mode, DTS creates a trigger named dts_cdc_sync_ddl, a heartbeat table named dts_sync_progress, and a DDL history table named dts_cdc_ddl_history and enables CDC for the source database and specific tables. We recommend that you set the maximum number of records per second to 1,000 for the tables for which CDC is enabled in the source database. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses the read and write resources of the source database and destination cluster. This may increase the loads on the database servers. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the size of used tablespace of the destination database is larger than that of the source database. You must make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the `ROUND(COLUMN,PRECISION)` function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for columns of the FLOAT data type to 38 digits and the precision for columns of the DOUBLE data type to 308 digits. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination database, you must stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination database after the failed task is resumed. If the data migration task involves incremental data migration, DTS does not allow you to perform the reindexing operation. If you perform the reindexing operation, the data migration task may fail and data loss may occur. Note DTS cannot migrate DDL operations related to the primary key of a table for which CDC is enabled. If the number of CDC-enabled tables to be migrated in a single migration task exceeds 1,000, the precheck fails. To perform incremental data migration, you must disable the trigger and foreign keys in the destination database. Otherwise, the data migration task fails.
Special cases	If the source instance is an ApsaraDB RDS for SQL Server instance, DTS automatically creates an account named `rdsdt_dtsacct` on the ApsaraDB RDS for SQL Server instance. This account is used for data migration. Do not delete this account or change the password of this account when your data migration task is running. Otherwise, the task may fail. For more information, see System accounts. If the destination instance is an ApsaraDB RDS for SQL Server instance, DTS automatically creates a destination database in the destination instance. However, if the name of the database to be migrated does not conform to the naming convention of the destination ApsaraDB RDS for SQL Server instance, you must manually create a database in the destination instance before you configure the data migration task. For more information, see Create a database.

Billing

Migration type	Instance configuration fee	Internet traffic fee
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 Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Schema migration
DTS migrates the schemas of required objects from the source database to the destination database.
Full data migration
DTS migrates the historical data of the selected objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications.

SQL operations that support incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE Note If an UPDATE operation updates only the large fields, DTS does not migrate the operation.
DDL	ALTER TABLE, including only ADD COLUMN, DROP COLUMN, and RENAME COLUMN CREATE TABLE and CREATE INDEX Note If a CREATE TABLE operation creates a partitioned table or a table that contains functions, DTS does not migrate the operation. DROP TABLE RENAME TABLE TRUNCATE TABLE Note DTS does not migrate transactional DDL operations. For example, DTS does not migrate an SQL operation that contains DDL operations on multiple columns or an SQL operation that contains both DDL operations and DML operations. Data loss may occur after such SQL operations are migrated. DTS does not migrate DDL operations that contain user-defined types. DTS does not migrate online DDL operations. DTS does not migrate DDL operations performed on objects whose names contain reserved keywords. DTS does not migrate DDL operations performed in system stored procedures. If the source database uses the hybrid log-based parsing mode, all common DDL operations can be migrated.

Permissions required for database accounts

Database type	Schema migration	Full data migration	Incremental data migration	References
Source instance	The SELECT permission	The SELECT permission	The owner permission on the objects to be migrated	For more information, see Create databases and accounts.
Destination instance	Read and write permissions	Read and write permissions	Read and write permissions	For more information, see Create databases and accounts.

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, move the pointer over DTS.
3. Choose DTS (DTS) > Data Migration.
Note
- The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
- You can also go to the Data Migration page of the new DTS console.
From the drop-down list on the right side of Data Migration Tasks, select the region in which your data migration instance resides.
Note
If you use the new DTS console, select the region in which the data migration instance resides in the top navigation bar.
Click Create Task to go to the task configuration page.
Optional. In the upper-right corner of the page, click New Configuration Page.
Note
- Skip this step if the Back to Previous Version button is displayed in the upper-right corner of the page.
- Specific parameters in the new and previous versions of the configuration page may be different. We recommend that you use the new version of the configuration page.

Configure the source and destination databases. The following table describes the parameters.

Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to specify a unique task name.
Source Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must configure the following database information.
	Database Type	The type of the source database. Select SQL Server.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source ApsaraDB RDS for SQL Server instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether data is migrated across Alibaba Cloud accounts. In this example, No is selected.
	RDS Instance ID	The ID of the source ApsaraDB RDS for SQL Server instance.
	Database Account	The database account of the source ApsaraDB RDS for SQL Server instance. For more information about the required permissions, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the source database. Select Non-encrypted or SSL-encrypted based on your business requirements. If SSL encryption is disabled for the source database, select Non-encrypted. If SSL encryption is enabled for the source database, select SSL-encrypted. By default, DTS trusts the server certificate.
Destination Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must configure the following database information.
	Database Type	The type of the destination database. Select SQL Server.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination ApsaraDB RDS for SQL Server instance resides.
	Instance ID	The ID of the destination ApsaraDB RDS for SQL Server instance.
	Database Account	The database account of the destination ApsaraDB RDS for SQL Server instance. For more information about the required permissions, see the Permissions required for database accounts section of this topic.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the destination database. Select Non-encrypted or SSL-encrypted based on your business requirements. If SSL encryption is disabled for the destination database, select Non-encrypted. If SSL encryption is enabled for the destination database, select SSL-encrypted. By default, DTS trusts the server certificate.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the IP address whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the self-managed database is hosted on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the IP address whitelist of the database to allow DTS to access the database. For more information, see the CIDR blocks of DTS servers section of the Add the CIDR blocks of DTS servers topic.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated.

On the Select Objects page, configure the objects that you want to migrate.

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. Note If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Method to Migrate Triggers in Source Database	The method that is used to migrate triggers from the source database. You can select a migration method based on your business requirements. If no triggers are to be migrated, you do not need to configure this parameter. For more information, see Synchronize or migrate triggers from the source database. Note This parameter is available only if you select both Schema Migration and Incremental Data Migration for the Migration Types parameter.
SQL Server Incremental Synchronization Mode	Log-based Parsing for Non-heap Tables and CDC-based Incremental Synchronization for Heap Tables (Hybrid Log-based Parsing): Advantages: This mode supports heap tables, tables without primary keys, compressed tables, and tables with computed columns. This mode provides higher stability and a variety of complete DDL statements. Disadvantages: DTS creates the trigger dts_cdc_sync_ddl, the heartbeat table dts_sync_progress, and the DDL storage table dts_cdc_ddl_history in the source database and enables change data capture (CDC) for the source database and specific tables. You cannot execute the SELECT INTO or TRUNCATE statement on tables with CDC enabled in the source database. Triggers created by DTS in the source database cannot be manually deleted. Incremental Synchronization Based on Logs of Source Database (Heap tables are not supported): Advantages: This mode does not modify the settings of the source database. Disadvantages: This mode does not support heap tables, tables without primary keys, compressed tables, or tables with computed columns. Polling and querying CDC instances for incremental synchronization: Advantages: Full data migration and incremental data migration are supported if the source database is an Amazon RDS for SQL Server instance, a database in Microsoft Azure SQL Database, a Microsoft Azure SQL Managed Instance, a Microsoft Azure SQL Server on Virtual Machine, or a Google Cloud SQL for SQL Server instance. If you use the native CDC component of SQL Server to obtain incremental data, incremental migration is more stable and occupies less network bandwidth. Disadvantages: The source database account that is used by the DTS instance must have the permission to enable CDC. Incremental data migration takes about 10 seconds. If you migrate multiple tables in multiple databases, stability and performance issues may occur.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select columns, tables, or schemas as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects, such as views, triggers, or stored procedures, to the destination database.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be migrated. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions. To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information about the SQL operations that support incremental migration, see the SQL operations that support incremental migration section of this topic.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, you do not need to configure this parameter.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure the data verification task.
For more information about how to use the data verification feature, see Configure a data verification task.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.
Wait until Success Rate becomes 100%. Then, click Next: Purchase Instance.

Purchase a data migration instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.