SDRS Concepts

Production site

Data center that independently runs services in normal cases. In asynchronous replication, the production site refers to your on-premises data center or the location where your ECSs reside. In synchronous replication, the production site refers to the AZ where your servers reside. It is specified when you create protection groups.

Disaster recovery site

Data center that does not run services when the production site works properly. It is used to back up data in real time. When the production site fails (planned or unexpected), the disaster recovery site can take over services after a switchover or failover. It can reside in the same city as the service management center or in another city.

The production site and disaster recovery site must be in two AZs of a same region.

Protection group

Manage the servers you want to replicate. One protection group manages servers in one VPC. If you have multiple VPCs, create multiple protection groups.

Protected instance

A protected instance consists of one server and its replicated server. One protected instance belongs to one protection group only. The AZs of instance servers are the same as those of the protection group's production site and disaster recovery site.

VBD

Virtual Block Device (VBD) is the default device type of EVS disks. VBD EVS disks support only basic SCSI read/write commands. This disk type is suitable for enterprise office applications as well as development and testing.

SCSI

Small Computer System Interface (SCSI) is another EVS device type. SCSI EVS disks support transparent SCSI command transmission and allow the server OS to directly access the underlying storage media. In addition to basic SCSI read/write commands, SCSI EVS disks support advanced SCSI commands, such as persistent SCSI reservations, which are used for clustered applications to guarantee data security.

RPO

Recovery point objective. It is a service switchover policy with minimal data loss. Data recovery points are used as objectives to ensure that the data used for disaster recovery switchovers is the latest backup data.

RTO

Recovery time objective. It is the target time spent for critical services to recover to an acceptable level. RTO is set to minimize the impacts on the services. In SDRS, RTO refers to the period of time from when you perform a switchover or failover at the production site to the time when the servers at the disaster recovery site start to run. This period does not include the time spent on DNS configuration, security group configuration, or customer script execution, and is within 30 minutes.

Disaster recovery drill

Verify that disaster recovery site servers can take over services from production site servers after a failover.

By running disaster recovery drills, you can simulate recovery scenarios and formulate recovery plans. When a fault occurs, you can use the plans to recover services as quickly as possible.

Replica pair

A replica pair consists of a production site and a disaster recovery site. The replication relationship is established between two sites.

Cloud disaster recovery gateway

Aggregate and compress data on all replicated production site servers, and synchronize the data to the disaster recovery site.

Proxy client

Transmit data on the server to the cloud disaster recovery gateway.

Enabling protection

If services are running at the production site and the data synchronization stops, you can enable protection to start data synchronization.

Failover

A failover switches the services from the production site to the disaster recovery site. After a failover, data synchronization stops and the protected instance status changes to Failover completed.

Failback

After a failover, services are running at the disaster recovery site. You can fail back to your production site with a failback. After the failback, data synchronization stops.

Reverse reprotection

After a failover, data is not automatically synchronized from the disaster recovery site to the production site, and protection is disabled for protected instances. To start data synchronization from the disaster recovery site to the production site, perform a reverse reprotection.

Reprotection

After a failback, data is not automatically synchronized from the production site to the disaster recovery site, and protection is disabled for protected instances. To start data synchronization from the production site to the disaster recovery site, perform a reprotection.

Disabling protection

If services are running at the production site, and data synchronization is in progress or completed, you can disable protection to stop data synchronization.

Replication pair

A replication pair consists of one EVS disk and its replicated disk. One replication pair belongs to one protection group and can be attached to a protected instance in this group.

Switchover

Temporarily stop servers at the production site and switch over services to the disaster recovery site for planned outages. After a switchover, the disaster recovery direction is from the disaster recovery site to the production site. Servers and EVS disks at the disaster recovery site are ready to start.

Failover

A failover forcibly stops the servers and disks at the production site and sets the servers and disks at the disaster recovery site to ready-to-start state. This operation affects all the protected instances in the protection group. After a failover, you need to manually start the servers at the disaster recovery site. In addition, the protection group status changes to Failover complete, and data synchronization of the protection group stops. You need to enable reprotection to recover data synchronization.

Enabling protection

Protection can be enabled after a protection group is created or data synchronization stops. Once protection is enabled, data synchronization starts, and you can view the synchronization progress on the console. This operation affects all the protected instances and replication pairs in the protection group.

After you click Enable Protection, the status of the protection group changes to Synchronizing, and Disable Protection is not available.

Reprotection

Reprotection can be enabled after a failover. Once reprotection is enabled, data synchronization starts, and you can view the synchronization progress on the console. This operation affects all the protected instances and replication pairs in the protection group.

After you click Reprotect, the status of the protection group changes to Reprotecting, and Disable Protection becomes unavailable.

Disabling protection

Protection can be disabled after data synchronization of a protection group is complete. After disabling protection, the status of the protection group changes to Available.

Attaching a replication pair

Attach the two disks in a replication pair to the servers in a protected instance.

Detaching replication pair

Detach the two disks in a replication pair from the servers in a protected instance.

Disaster recovery direction

Data replication direction. After you create a protection group, data is replicated from the production site to the disaster recovery site.

A switchover or failover changes the disaster recovery direction of a protection group.

Protection group status

Status of a protection group, after you create, delete, switch over, fail over, enable protection for, or disable protection for a protection group.

For details, see Protection Group Status.

Synchronization status

Data replication status between the production and disaster recovery sites.

VPC

VPC of the protection group. A VPC facilitates internal network management and configuration, allowing secure and quick modifications to networks. By defaults, servers in the same VPC can communicate with each other, but those in different VPCs cannot.