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SDRS Concepts

Table 1 SDRS concepts

Concept	Description
Production site	Data center that independently runs services in normal cases. For SDRS, it is the AZ where your servers locate. This parameter is specified when you create a protection group.
DR 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 DR 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, you need to 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 DR site.
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 DR site for planned outages. After the switchover, data synchronization continues, but the DR direction is changed (from the DR site to the production site). Servers and disks at the DR 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 DR 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 DR 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	Can be performed after the data synchronization is complete. Once the protection is disabled, the data synchronization stops, and the protection status of the protection group changes to Available.
Attaching a replication pair to a protected instance	Attach the two disks in a replication pair to the servers in a protected instance.
Detaching a replication pair from a protected instance	Detach the two disks in a replication pair from the servers in a protected instance.
DR direction	Data replication direction. After you create a protection group, data is replicated from the production site to the DR site. After you perform a switchover, services at the production site are switched to the DR site, and services at the DR site are switched over to the production site.
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 section "Protection Group Status" in the Appendixes of Storage Disaster Recovery Service API Reference.
Synchronization status	Data replication status between the production and DR 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.
VBD	Virtual Block Device (VBD) is the default disk device type. VBD disks only support basic Small Computer System Interface (SCSI) read/write commands. Such disks are suitable for enterprise office applications as well as development and test environments.
SCSI	SCSI is another disk device type. SCSI disks support transparent SCSI command transmission, which allows the server OS to directly access the underlying storage media. In addition to basic SCSI read/write commands, SCSI 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 DR 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. For 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.
DR drill	Verify that DR site servers can take over services from production site servers after a failover. By running DR 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.

Parent topic: Basic Concepts