This topic describes the limits on the async replication feature of Hybrid Disaster Recovery (HDR).
Limits on regions and zones
More regions will be supported in the future. The regions that are available when you create a site pair are the definitive list. The async replication feature is supported in the following regions and zones:
China (Hangzhou): Zone B, Zone F, Zone G, Zone H, Zone I, Zone J, and Zone K
China (Shanghai): Zone B, Zone E, Zone F, Zone G, Zone K, Zone L, Zone M, and Zone N
China (Qingdao): Zone B and Zone C
China (Beijing): Zone D, Zone F, Zone G, Zone H, Zone I, Zone J, Zone K, and Zone L
China (Zhangjiakou): Zone A, Zone B, and Zone C
China (Hohhot): Zone A and Zone B
China (Ulanqab): Zone A, Zone B, and Zone C
China (Shenzhen): Zone C, Zone D, Zone E, and Zone F
China (Heyuan): Zone A and Zone B
China (Guangzhou): Zone A and Zone B
China (Chengdu): Zone A and Zone B
China (Hong Kong): Zone B, Zone C, and Zone D
Singapore: Zone A, Zone B, and Zone C
Japan (Tokyo): Zone A, Zone B, and Zone C
South Korea (Seoul): Zone A
Philippines (Manila): Zone A
Thailand (Bangkok): Zone A and Zone B
Malaysia (Kuala Lumpur): Zone A, Zone B, and Zone C
Indonesia (Jakarta): Zone A, Zone B, and Zone C
Germany (Frankfurt): Zone A, Zone B, and Zone C
UK (London): Zone A and Zone B
US (Silicon Valley): Zone A and Zone B
US (Virginia): Zone A and Zone B
UAE (Dubai): Zone A and Zone B
SAU (Riyadh - Partner Region): Zone A and Zone B
China East 2 Finance Cloud: Zone G, Zone K, and Zone Z
South China 1 Finance Cloud is available in Zone B, Zone D, and Zone E.
(Invitational preview) China (Beijing) Finance Cloud: Zone L and Zone K
Alibaba Finance Cloud and the Alibaba Cloud public cloud are isolated from each other. Async replication for disaster recovery cannot be performed between them.
Limits on specifications and ECS disks
The following table describes the limits on specifications that apply to the async replication and replication pair-consistent group features.
Item | Description |
Number of replication pairs that can be created per disk | 1 |
Number of replication pairs that can be added per replication pair-consistent group | 17 |
Replication cycle | 15 minutes (Data is asynchronously replicated from a primary disk to a secondary disk every 15 minutes.) |
Replication rate | The replication rate can be up to 100 MB/s and may vary based on the system load. |
Primary disk category | Primary disks must be ESSDs or ESSD AutoPL disks. |
Secondary disk category | Secondary disks must be of the same disk category and have the same performance level and capacity as the corresponding primary disks. |
The following table describes the limits on disks that apply to the async replication and replication pair-consistent group features.
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 the recovery point objective (RPO), the data of a snapshot created for a primary disk may be inconsistent with that of a snapshot created at the same time for the associated secondary disk.
③: Replication is restricted to encrypted disks. Cross-replication between encrypted disks and unencrypted disks is not supported.
Item | Supported by the primary disk | Supported by the secondary disk |
Read and write operations | √ | ×① |
Disk deletion | × | × |
Disk initialization | × | × |
Disk resizing | × | × |
Disk attaching | √ | × |
Snapshot creation | √ | ✓② |
Rollback based on snapshots | √ | × |
Disk category change | × | × |
Performance level change | × | × |
Disk encryption | √ | ✓③ |
Multi-attach | × | × |
Disk migration together with instances | × | × |
Limits on ECS networks
The following limits apply to Elastic Compute Service (ECS) networks:
A single network interface card (NIC) has the following limitations:
After a failover, the primary ENI cannot be automatically configured for some operating systems at the disaster recovery site. After these operating systems are started at the disaster recovery site, you must configure the primary ENI. For more information, see Configure a secondary ENI.
The following limitations apply to multiple network interface cards:
After a secondary ENI is bound to an ECS instance, some images cannot automatically identify the IP address of the secondary ENI or add a route. As a result, the secondary ENI cannot work properly.
If an ECS instance is configured with a secondary ENI, check the IP address of the secondary ENI after a failover to ensure that the secondary ENI works as expected. For more information, see Configure a secondary ENI.
Sites do not support elastic network interfaces (ENIs) or ECS instances outside a VPC.
Limits on configuration quotas
A single user can create a maximum of 1,000 disaster recovery site pairs.
Each disaster recovery site pair supports a maximum of 512 protection groups.
Each protection group supports a maximum capacity of 32 TB and a maximum of 17 disks.
Limits on consistency guarantee
The async replication feature supports only crash consistency and does not support application consistency. For applications and databases that have high requirements for consistency, we recommend that you configure direct writes of data to disks based on application and database documentation. This ensures data consistency and reduces the risk of extended recovery time due to asynchronous data writes when a disaster occurs.