High availability consists of a series of modes in which Adaptive Server runs during its operation. There are two types of modes, stable and transitional. A stable mode is a system state in which Adaptive Server can exist for an extended period of time, such as the day-to-day operation of Adaptive Server.
Stable modes include:
Single-server mode
Normal companion mode
Failover mode
Suspended companion mode
The failback transitional mode occurs when Adaptive Server shifts from failed over mode to normal companion mode. The failback transitional mode is typically of a very short duration. The different modes and the movement that the primary companion makes while changing modes are shown in Figure 4-1:
Figure 4-1: Modes of operation for high availability
Before you can configure two Adaptive Servers as companions, both must be in single-server mode, which is the default mode of a newly installed Adaptive Server after running installhasvss. After you configure the Adaptive Servers as companions, they are in one of three stable modes:
Normal companion mode
Failed-over mode
Suspended companion mode
