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OceanStor 18500, 18800, and 18800F Storage System V100R001C30 Remote Replication Feature Guide 09

This document describes the remote replication feature, in terms of the implementation principle, application scenario, configuration process, and reference information.
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Service Switchover

Service Switchover

When a disaster occurs at the primary site of a remote replication session, the secondary site can quickly take over primary site services to ensure business continuity.

The remote replication feature not only implements remote data backup but also recovers services as soon as possible in the case of a disaster to keep service continuity. The following two indicators need to be considered before a service switchover:

  • RPO

    The maximum acceptable amount of time prior to a disaster wherein changes to data may be lost. Data changes preceding the disaster by longer than this amount of time are preserved via recovery. Synchronous remote replication copies data from a primary LUN to a secondary LUN in real time, ensuring that the Recovery Point Objective (RPO) is 0. Zero is a valid value and meets the "zero data loss" requirement. A remote disaster recovery system built based on synchronous remote replication implements data-level disaster recovery with a high disaster recovery level (tier 6—zero data loss). In asynchronous remote replication scenarios, the RPO is the time that you set for Interval.

  • RTO

    The maximum acceptable amount of time required to return one or more applications and associated data to a normal operational state after a disaster. The indicated recovery time serves as the objective and ensures that the standby host takes over services as quickly as possible. The Recovery Time Objective (RTO) depends on host services and disasters in remote replication scenarios.

Choose the remote replication mode based on the RPO and RTO requirements of users.

Service Switchover Through Remote Replication

Services can run on the secondary storage system only when the following conditions are met:
  • Historical service data exists in the secondary storage system.
  • Services on the production host have also been configured on the standby host.
  • The secondary storage system allows a host to access a LUN in a LUN group mapped to the host.
When a disaster occurs at the primary site, the remote replication links between the primary LUN and the secondary LUN go down. If this occurs, the administrator needs to manually change the access permission of secondary LUNs to accessible to enable a service switchover. Figure 1-4 shows how a service switchover is implemented through remote replication.
Figure 1-4  Service switchover through remote replication

NOTE:
After a primary/secondary switchover, the respective primary and secondary sites record changed data to avoid full synchronization when the secondary site becomes the primary site.
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Updated: 2019-01-28

Document ID: EDOC1000077758

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