Answers to common questions about data migration and data synchronization for Tair and Redis instances using Data Transmission Service (DTS).
What are data migration and data synchronization?
Data migration copies key-value pairs from a Tair or open source Redis instance to another Tair or open source Redis instance. The task runs once and stops automatically after all data is transferred. Use it when you need a one-time, bulk transfer—for example, moving data from a self-managed Redis instance to a Tair instance on Alibaba Cloud.
Data synchronization continuously replicates key-value pairs from a source instance to a destination instance in real time. The task keeps running to maintain data consistency between the two instances. Use it when you need ongoing replication—for example, for active geo-redundancy or disaster recovery.
Both operations replicate data to the destination instance without affecting the source instance.
How do data migration and data synchronization work?
Both features rely on DTS to capture and apply changes between instances. For a detailed explanation of the underlying architecture, see System architecture and design concepts.
What is the difference between data migration and data synchronization by using DTS?
The table below compares key dimensions to help you choose the right approach.
DTS data synchronization supports more Tair scenarios and features than data migration. If your use case allows, prefer data synchronization. For more information, see Data synchronization.
| Dimension | Data migration | Data synchronization |
|---|---|---|
| Typical use case | One-time transfer from on-premises databases, self-managed databases on ECS instances, or third-party cloud platforms to Tair instances on Alibaba Cloud | Continuous, real-time replication between Tair instances—for active geo-redundancy, disaster recovery, or data analytics |
| Supported scenarios | Support for data migration | Support for data synchronization |
| Key features | Supports migration across self-managed databases in virtual private clouds (VPCs) owned by different Alibaba Cloud accounts | Supports duplicate keys handling modes, bidirectional synchronization between instances, and data synchronization across self-managed databases in VPCs owned by different Alibaba Cloud accounts |
| Billing | Schema migration and full data migration are free. Incremental data migration (optional) is billed by duration (regardless of the amount of data migrated); only pay-as-you-go is supported. | Schema migration and full data migration are free. After incremental migration starts, billing is by duration; both pay-as-you-go and subscription are supported. |
What do I do if an error occurs during a precheck?
Before a migration or synchronization task starts, DTS runs a precheck on the source and destination databases to confirm the task can proceed. If the precheck fails, consult the following resources to identify and fix the issue: