DR Overview

To prevent service unavailability caused by regional faults, DRS provides disaster recovery to ensure service continuity. You can easily implement disaster recovery between on-premises and cloud, without the need to invest a lot in infrastructure in advance.

The disaster recovery architectures, such as two-site three-data-center and two-site four-data center, are supported. A primary/standby switchover can be implemented by promoting a standby node or demoting a primary node in the disaster recovery scenario.

Figure 1 Real-time DR switchover

Figure 2 Dual-active DR principles

Loopback Prevention (DML)

When logs are parsed from the source database, the parsed data may contain a certain tag. The data containing the tag is written to the source database through DRS. The data written by applications is not tagged. After the parsing, the data without the tag is filtered out.
When data is replayed to the destination database, the data to be replayed is marked with a special tag, which is recorded in database logs.

Supported Database Types

The following table lists the database types supported by DRS.

**Table 1** DR schemes
Service Database	DR Database	Documentation
On-premises MySQL databases MySQL databases on an ECS MySQL databases on other clouds RDS for MySQL	RDS for MySQL	From MySQL to MySQL (Single-Active DR) From MySQL to MySQL (Dual-Active DR)
	GaussDB(for MySQL)	From MySQL to GaussDB(for MySQL) (Single-Active DR)
DDM	DDM	From DDM to DDM (Single-Active DR)
GaussDB(for MySQL)	GaussDB(for MySQL)	From GaussDB(for MySQL) to GaussDB(for MySQL) (Single-Active DR) From GaussDB(for MySQL) to GaussDB(for MySQL) (Dual-Active DR)

Basic Principles of Real-Time Disaster Recovery

DRS uses the real-time replication technology to implement disaster recovery for two databases. The underlying technical principles are the same as those of real-time migration. The difference is that real-time DR supports forward synchronization and backward synchronization. In addition, disaster recovery is performed on the instance-level, which means that databases and tables cannot be selected.

Next topic: DR Scenarios