Async replication is a feature that protects data across regions based on the data replication capability of Elastic Block Storage (EBS). This feature can asynchronously replicate data from a disk in one region to a disk in another region for geo-disaster recovery. You can use this feature to implement disaster recovery for critical business to protect data in your databases and improve business continuity.

Overview

Note The async replication feature is supported in the China (Shanghai), China (Beijing), China (Heyuan), and China (Chengdu) regions.
The async replication feature can asynchronously replicate data from an enhanced SSD (ESSD) (primary disk) in one region to an ESSD (secondary disk) that has the same specifications in another region. If the primary disk fails, you can fail over to the secondary disk. After the primary disk recovers, you can restore data from the secondary disk. The following figure shows the logic of the async replication feature.功能介绍
You can perform the async replication-related operations described in the following table.
Feature Description References
Create a replication pair Before you can use the async replication feature to implement geo-disaster recovery, you must create a replication pair. Create a replication pair
Activate async replication After you create a replication pair, you must activate the async replication feature for the pair so that data can be replicated from the primary disk to the secondary disk on a periodic basis. Activate async replication
Implement disaster recovery After you create and activate a replication pair, if the primary disk fails, you can use the failover and reverse replication sub-features of async replication to implement disaster recovery. Implement disaster recovery
Delete a replication pair The functionality of disks in a replication pair is limited. If a replication pair is no longer needed, you can delete it. Delete a replication pair
The following table describes the terms related to the async replication feature.
Term Description
asynchronous replication The async replication feature supports only asynchronous replication. Unlike synchronous replication, asynchronous replication replicates data from a disk in one region to a disk in another region on a periodic basis. In asynchronous replication, the data on the source disk may be inconsistent with that on the destination disk.
primary disk The disk from which to replicate data for disaster recovery. The primary disk is also called the source disk.
secondary disk The disk to which to replicate data. The secondary disk is also called the destination disk.
recovery point objective (RPO) The amount of data that may be lost due to a disk exception. RPO is measured by time. It is used as a data metric and holds a fixed value of 15 minutes in async replication. This value indicates that data written to a primary disk from up to 15 minutes prior may be lost when an exception occurs on the disk.
recovery time objective (RTO) The duration of time that it takes for a primary disk to recover after an exception occurs on the disk. RTO is used as a data metric in async replication. For example, if the value of RTO is 1 hour, it indicates that a primary disk can have its data restored and be back in service within 1 hour after an exception occurs on the disk.
replication pair The relationship that is established between a primary disk and a secondary disk, and the configurations for asynchronous replication.
failover A sub-feature of async replication that allows you to enable read and write permissions on the secondary disk and fail over to the disk.
reverse replication A sub-feature of async replication that can reverse replication relationships to replicate data from secondary disks to primary disks.

Billing

You are charged for the use of async replication on a subscription basis and must pay bandwidth fees.

Use scenarios

The async replication feature is suitable for users that require high data security and need to implement disaster recovery and cross-region-migration of business data.
  • Disaster recovery scenario
    If the primary disk in a replication pair fails, you can use the failover sub-feature to switch the primary and secondary disks over. During this switchover, the failover sub-feature disconnects the original replication link and fails services over to the disaster recovery system by attaching the new primary disk (original secondary disk) to the disaster recovery instance. Failover scenario
  • Cross-region migration scenario
    If you want to migrate your business data across regions, you can use the reverse replication sub-feature, instead of the image or snapshot replication feature. Reverse replication scenario

Limits

The following table describes the quotas used for the async replication feature.
Item Limit
Replication pairs that can be created per zone in an Alibaba Cloud account 16
Replication pairs that can be created for a single disk 1
Replication cycle 15 minutes (Data is asynchronously replicated from a primary disk to a secondary disk every 15 minutes.)
Primary disk category A primary disk must be an ESSD used as a data disk and uses the pay-as-you-go billing method.
Secondary disk category A secondary disk must be of the same disk category and have the same performance level and capacity as the associated primary disk.
The limits described in the following table apply to primary and secondary disks when you use the async replication feature.
Item Support by the primary disk Support by the secondary disk
Read and write operations ×
Disk deletion ×
Disk initialization × ×
Disk resizing × ×
Disk attaching ×
Snapshot creation
Rollback based on snapshots ×
Disk category change × ×
Performance level change × ×
Disk encryption × ×
Multi-attach × ×
Disk migration along with instances × ×
Note:
  • ①: After a replication pair is activated, the secondary disk enters the read-only state and no users have write permissions on the disk.
  • ②: Due to RPO, data of a snapshot created for a primary disk may not be consistent with that of a snapshot created at the same time for the associated secondary disk.