数据复制与AA双活（1）

最开始有些概念需要弄明白：

1. 什么是RPO？

Wiki： https://en.wikipedia.org/wiki/Recovery_point_objective

A recovery point objective, or “RPO”, is defined by business continuity planning. It is the maximum targeted period in which data might be lost from an IT service due to a major incident.

2. 什么是RTO？

Wiki: https://en.wikipedia.org/wiki/Recovery_time_objective

The recovery time objective (RTO) is the targeted duration of time and a service level within which a business process must be restored after a disaster (or disruption) in order to avoid unacceptable consequences associated with a break in business continuity.

3. 什么是Failover？

Wiki：https://en.wikipedia.org/wiki/Failover

Failover is switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application, server, system, hardware component, or network. Failover and switchover are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention.

RPO and RTO objectives can be met at the application, infrastructure, or hardware level, with different compromises and tradeoffs with each technology. Large enterprises use a combination of methods for meeting all of their objectives.